And even if it still did mean "gigantic screen with impeccable quality controls" like in the days of old, it still wouldn't matter!
And that's because a trademark is exclusive rights over using the name for a commercial purpose. So the IMAX folks could make a product called IMAX-VR if they made a VR headset. But the Oculus folks, if they got some 8k phone screen, couldn't call it Oculus-IMAX without a licensing agreement, because IMAX owns the name IMAX with respect to product names.
But owning it with respect to product names doesn't mean you can prevent people from using it at all. How else would Coke (tm) be able to tell you in a commercial how much better they are than Pepsi (tm) as a result of some ridiculously staged "public tastings" where regular people prefer Coke (tm) to Pepsi (tm) three to one?
Anyone can refer to someone else's trademarked product name full stop. The only thing a trademark does is prevent other people from naming their products the same as, or confusingly similar to, the one which was trademarked first. And if someone thinks their new product name is different enough to be confusing the trademark holder still has to take them to court to prove it.
Yup, IMAX's "MPX" is little more than a largeish movie screen, with typical sizes around 18m by 8.5m (58' by 28'). MPX maxes out under the size of a "classical IMAX" display, and as far as I can see it exists just about solely so multiplexes can tack on additional IMAX surchages on your ticket.
Yes this is frustrating. They just closed one of the only large IMAX screens in lower NY at the Palisades Mall in West Nyack, NY which is where most people from northern jersey and lower NY went. The IMAX is moving to the multiplex in the same mall - thus it will be the smaller screen variety.
We're left with Lincoln square in NYC and possibly New Rochelle, NY as the only remaining large format IMAX in the area.
It used to mean that, not any more. IMAX screens are allowed to be much, much smaller than before.