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Defining "serious consideration" as meaning congressional debate and "structure of Rome" as a plurity, yes, they proposed and discussed a plural executive (or what Dr Franklin called a "cabal") several times. Most notably these discussions occured in the Congress of 1775 and again when discussing the Virginia Plan in 1787.
July 21 1775 Ben Franklin presents to Congress a proposal for a new government charter of a free America. Article IX of his plan outlines an executive committee formed by (and from) congressional members;
Article IX. An executive Council shall be appointed by the Congress out of their own Body, consisting of 12 Persons; of whom in the first Appointment one Third, 4, shall be for one Year, 4 for two Years, and 4 for three Years; and as the said Terms expire, the vacancies shall be filled by Appointments for three Years, whereby One Third of the Members will be changed annually. And each Person who has served the said Term of three Years as Counsellor, shall have a Respite of three Years, before he can be elected again. This Council of whom two thirds shall be a Quorum in the Recess of the Congress is to execute what shall have been enjoin’d thereby; to manage the general foreign Business and Interests to receive Applications from foreign Countries; to prepare Matters for the Consideration of the Congress; to fill up (pro tempore) continental Offices that fall vacant; and to draw on the General Treasurer for such Monies as may be necessary for general Services, and appropriated by the Congress to such Services.
The Roman system was a two-person single year term without reelection and allowed much more authority, but the ideas are quite similar. It did not pass Congress but Franklin would continue to pursue a plural executive as a result of seeing abuses of a singular one in Pennsylvania. Other founders strongly agreed with him.
On June 1st 1787 according to Madison's Notes, with my emphasis bolded and my additions in (parenthesis);
The Committee of the Whole proceeded to the seventh Resolution, that a National Executive be instituted, to be chosen by the National Legislature for the term of — years, &c., to be ineligible thereafter, to possess the Executive powers of Congress, &c (The "Virginia Plan" proposed executive)
Mr. PINCKNEY was for a vigorous Executive, but was afraid the executive powers of the existing Congress might extend to peace and war, &c.; which would render the Executive a monarchy of the worst kind, to wit, an elective one.
Mr. WILSON moved that the Executive consist of a single person. Mr. C. PINCKNEY seconded the motion, so as to read “that a National Executive, to consist of a single person, be instituted.”
A considerable pause ensuing, and the Chairman asking if he should put the question, Doctor FRANKLIN observed that it was a point of great importance, and wished that the gentlemen would deliver their sentiments on it before the question was put. (Here Franklin recognizes the significance and, although he certainly sides with a plural executive, simply begs the debate begin without offering direction or opinion on the matter)
Mr. RUTLEDGE animadverted on the shyness of gentlemen on this and other subjects. He said it looked as if they supposed themselves precluded, by having frankly disclosed their opinions, from afterwards changing them, which he did not take to be at all the case. He said he was for vesting the executive power in a single person, though he was not for giving him the power of war and peace. A single man would feel the greatest responsibility, and administer the public affairs best.
Mr. SHERMAN said, he considered the executive magistracy as nothing more than an institution for carrying the will of the legislature into effect; that the person or persons ought to be appointed by and accountable to the legislature only, which was the depository of the supreme will of the society. As they were the best judges of the business which ought to be done by the executive department, and consequently of the number necessary from time to time for doing it, he wished the number might not be fixed, but that the legislature should be at liberty to appoint one or more as experience might dictate.
Mr. WILSON preferred a single magistrate, as giving most energy, dispatch, and responsibility, to the office. He did not consider the prerogatives of the British monarch as a proper guide in defining the executive powers. Some of these prerogatives were of a legislative nature; among others, that of war and peace, &c. The only powers he considered strictly executive were those of executing the laws, and appointing officers, not appertaining to, and appointed by, the legislature.
Mr. GERRY favored the policy of annexing a council to the Executive, in order to give weight and inspire confidence.
Mr. RANDOLPH strenuously opposed an unity in the executive magistracy. He regarded it as the fœtus of monarchy. We had, he said, no motive to be governed by the British government as our prototype. He did not mean, however, to throw censure on that excellent fabric. If we were in a situation to copy it, he did not know that he should be opposed to it; but the fixed genius of the people of America required a different form of government. He could not see why the great requisites for the executive department, vigor, despatch, and responsibility, could not be found in three men, as well as in one man. The executive ought to be independent. It ought, therefore, in order to support its independence, to consist of more than one.
Mr. WILSON said, that unity in the Executive, instead of being the fœtus of monarchy, would be the best safeguard against tyranny. He repeated, that he was not governed by the British model, which was inapplicable to the situation of this country; the extent of which was so great, and the manners so republican, that nothing but a great confederated republic would do for it.
Mr. WILSON’S motion for a single magistrate was postponed by common consent, the Committee seeming unprepared for any decision on it; and the first part of the clause agreed to, viz. “that a national Executive be instituted.”
On Aug 6 they put together everything they had so far. Article X read;
Sec 1. The Executive power of the United States shall be vested in a single person. His style shall be, “The President of the United States of America,” and his title shall be, “His Excellency.” He shall be elected by ballot by the Legislature. He shall hold his office during the term of seven years; but shall not be elected a second time.
They eventually sent the plural debate to committee. On August 24 the general Congress;
Took up Article X, Section 1 (Executive):
Agreed on one Executive but defeated four different methods of electing the President including by the people (9 – 2) and by electors (6 – 5).