So stadium has a 64x64 base but how come this was never done for the other Environments? Was it hard to do?
Have not tried using the 64x64 in vanilla as i never really play stadium but i fiddled around with it in a titlepack.
Is it a mod that was implemented into the titlepack?
Ive heard about the now outdated unlimiters that where a thing back in early 2010´s etc but is this different from that or is it just a mod?

128x128 or 256x256 is kinda ridiculous since 32x32 is actually already quite big once you start making blocks smaller than 64x64 meters, but sometimes i feel like 64x64 would have been cool for things like Nascar maps that require large roads (makes it somewhat easier to add panoramic scenery i guess).
i know Nascar isnt really that popular but you know, can be kinda fun sometimes i guess.
Also Canyon rpg´s would have been kinda cool (i guess that is already feasible with 32x32 though).

I have no idea about other environments or base larger than 64x64, but here is my take on the base64 and nascar maps: in my opinion, base64 is good when you want to make very long nascar maps (more than 1 minutes per lap), which may happen for some endurance events. But I feel that it tends to create some issues if the mapper is not careful enough. In particular, it tends to create very long straights, and therefore turns that you reach at 600+ and therefore autodrifts, which I (personally) really dislike. This doesn't happen all the time (I think I did a good job at avoiding this issue for the few endurance maps I made), but still it may happen ^^ So for me (in my personal opinion), unless you go for an extra long nascar track, there is no need for the base64 [in nascar]