V8 in MR2 has been around for some time. Besides the Northstar-engined AW11 (the one u posted) there area at least two other projects going on right now. One is 1UZ-FE into AW11 in NZ and another is 1UZ-FE into SW20. Believe or not the AW11 engine bay is not tiny. It's cavernous in comparison to the engine bay of the SW20.
Keep in mind the problem of fitting another drivetrain into a particular car is not just the size of the engine. Have to remember the layout of the engine as well. It's possible to fit longitudal mounted engines be it 2JZ, 1JZ or 1UZ-FE into a ST185 since there is already space for the propshaft on the floorpan courtesy of the 4WD system.
When it comes to the new ZZT Celica's, they're designed purely for FWD drivetrain. To fit the propshaft and gearbox required would mean cutting up the floorpan. Not feasible for a road-going car.