As far as I understand it, during WWI and the Arab Revolt, many leaders wanted a united Arab state to be carved from the collapsing Ottoman Empire; a wish that would go unfulfilled due to European intervention among other things.
What were the suggested borders of the state as it was imagined during that time? Did it include places like Egypt and Sudan, even so far as Morocco? Or did it only stay in the Mesopotamian region?
While only able to answer on history that did happen, I will try to explain some aspects that made a united Arab state unlikely, at least one stretching outside of the Arab peninsula.
Firstly, Egypt's political establishment was at this time quite clearly separated from pan-Arab sympathies. Sa'd Zaghlul, leader of the Egyptian Wafd party and Prime Minister in 1924, said in reference to Arab unity “If you add one zero to another zero, then you add another zero, what will be the sum?” and “Our problem is an Egyptian problem, not an Arab problem”. While some, such as the 19th century ruler Ibrahim Pasha, expressed an Arab pride, much of Egyptian society did not see themselves as Arab in the early 20th century. At the time of the revolt, Egypt would most definitely not become a part of a united Arab state, and the Egyptian troops that did participate were on decision by the palace which was very much the puppet of Britain.
Even when it comes to the Arab peninsula and the Levant there was a divide stemming from the power struggle between the House of Hashim, whom ruled in the hijaz but later conquered by the Sauds who founded the Saudi Kingdom by uniting the Hijaz and the Najd. The House of Hashim continued to rule in Transjordan and do so still today, as you may know it is called the Hashemite Kingdom of Jordan.
However, their struggle against the Ottomans was unifying and the ideal was of course unity as well as independence, of at least the Hijaz, the Najd, and north up to Greater Syria. The British had already made clear that they would keep control of Aden (in Yemen) and the Syrian coast. But the Hashemite-Saud rivalry ultimately proved the united Arab state impossible.
Sources:
Chejne, Anwar G. "Egyptian Attituted toward Pan-Arabism." Middle East Journal (Middle East Institute) 11, no. 3 (1957) pp. 253-268.
Goldschmidt Jr., Arthur. "The Rise of Nationalism." In A Concise History of the Middle East, pp. 175-192. Boulder: Westview Press, 2002.
Jankowski, James. Egypt: A Short History, by James Jankowski, Oxford: Oneworld Publications, 2000.