A lot of Allied aircraft and armored vehicles arrived just around the end of the war. Aircraft like the Gloster Meteor and the P-80 Shooting Star, and tanks like the IS-3, T-44, Centurion, M26 Pershing, and the T95/28 superheavy tank, along with various prototype vehicles arrived just at the end (M26), arrived but saw no combat, (Centurion, Meteor, T-44), or were cancelled when the war ended (T95/28, T29-series heavy tanks).
Would these vehicles have been deployed into combat if the war had gone on longer?
For example, the M41 Walker Bulldog was deployed to Korea for combat testing even before it had been officially adopted and deployed.
Not necessarily. The Allies were not in the habit of deploying prototype weapons, because they usually end up ineffective. The real world is not Gundam or Japanese mecha anime. For a weapon to be effective it must be rigorously tested, its place in the entire army be properly defined, and soldiers trained to properly use it.
Most of the German "super weapons" were in fact highly ineffective because they were rushed into service without considering testing, doctrine, and training. The first deployment of the Panther tank for instance - at Kursk - was a fiasco with several Panthers setting themselves on fire from overheating before even seeing combat. The first Type XXI was completed in 1943, but conducted its first war cruise only in 1945 because the damn things kept leaking. The Me-262 first took flight in 1942, but was only "operational" by 1944 with engines that had only a few hours of service life.
And in any case the Meteor also became operational in 1944 - the German "lead" in jet fighters was fictional - and the only reason why they don't get as much press is because the Meteors were earmarked for the specialized role of intercepting V1 cruise missiles as no other Allied fighter was capable of this. There was no need to deploy them as frontline fighters to "counter" the Me-262; Allied prop plane fighters in fact found them such a novelty that some reports flat-out said they were competing to bring down 262s rather than being afraid of them!
In any case, no new weapon was likely to be deployed in significant numbers before August 1945, at which point the war definitively ends because of the ultimate actual secret weapon developed by the Allies - which is an atomic bomb dropped on an Axis capital.
The new M26 Pershing was to see wide use if the war continued. Supposing that Japan refused to surrender, or the atomic bombs hadn't been dropped or never even existed, and there had been an invasion of the Japanese mainland, the US Army planned to reorganize its tank battalions. In the proposed new July 1945 TO&E for a tank battalion, Companies A and C would have M4A3(76)W and M4A3(105), both with HVSS ("M4A3 tanks will have wide tracks") Company B would be equipped with M26 Pershings and M4A3(105). The light tank Company D would have M24 Chaffee.
The 706th and 767th Tank Battalions were to be organized differently; The 767th Tank Battalion would have all 4 companies equipped with Pershings and M4A3(105) HVSS. The 706th Tank Battalion would retain their light tank company, having 3 companies of Pershings and M4A3 (105) HVSS. Both battalions would also each get 10 flame-throwing tanks.
12 M26s were shipped to Okinawa and actually arrived on the island before the battle ended. They were divided up evenly between the 193rd and 711th Tank Battalions, but saw no combat. Well over 500 Pershings could have been eventually used during the invasion of Japan, due to each infantry division having its own attached tank battalion, and the planned employment of two armored divisions (US Army maps of operation Olympic and Coronet)
Unfortunately, the Pershing had sluggish off-road performance as it used basically the same engine as the M4A3 tank (500 hp Ford GAA V-8) The mountainous terrain and borderline greasy mud of Okinawa probably would not have been very kind to the Pershing; off-road performance would have been to its detriment in some undeveloped and rugged areas of the Japanese islands. Poor roads and weak bridges would have also been an issue.
The Fisher Body division of General Motors as well as Chrysler were contracted to produce 7,500 Pershings to completely replace the M4A3(76)W HVSS as the Army's primary battle tank as the invasion may have lasted years due to the anticipated ferocious resistance the Japanese would give; this fell through after the war thankfully ended, and only about 2,000 Pershings were built.
30 P-80A were waiting aboard an aircraft carrier in the Philippines for delivery to the 414th Fighter Group for anticipated use in the invasion of Japan, but several pieces of critical equipment never arrived, and as a result the P-80s were not used.
Sources:
http://the.shadock.free.fr/sherman_minutia/manufacturer/m4a376w/m4a3_76w.html
M26 Pershing 1943-1953, by Steven J. Zaloga
DOWNFALL: The End of The Imperial Japanese Empire, by Richard Frank