I can imagine there is some limit at some point where the engine might "collapse", at least I think so.
About limitation: In 1.3. I could not use several bigger background objects because of the lack of transparency (specially the SMW ghost house entry images), which is now possible. Of course an endless amount of objects would be kind of nice, but since I think the engine might "say" at one point "nope, not gonna load your map anymore, I gonna crash lol", it might be better to limit the custom graphics objects in terms of slots at one point: There is also not enough space in the "blocks and tiles" section, but maybe for an "custom" register.
If you look at Super Mario Maker we can count ourself lucky to be able to exchange block or bg graphics anyway. If you conserve your resources (max amount of blocks and background objects) well enough you should not have any big problems to archive the level you want to design. Normally Mario levels are supposed to repeat certain objects anyway, as a matter of design I think.
So to put it in a nutshell: We can NOW use ANY background objects with transparency which was not possible before.
The game engine has more than enough blocks to realize most of the levels we actually would like to design.
We can modify each graphics anyway, even for each level separately.
If you THEN have for example 32 additional graphics slots for blocks OR bg objects it should be more than enough for pretty much everything IMHO.
I think the programmer has to consider in advance what the engine can do before it collapses, therefore has to set hardcoded limits. Stress tests should guarantee that everything is working under hardest conditons and if you allow the user too much the engine might collapse at some point.
Of course this is what I think from my personal experience. This is not the first time I somehow "test" this kind of stuff. I already worked around 1,5 years as software tester in a company. There we also executed stress tests under these mentioned conditions.
Hey, or look at Sony and MS: I remember about reading an article, where it has been stated that an additonal core has been made available for games to use, which was locked before for the system only. I bet their stress tests resulted that they can "open" the additional core without worries of console problems at some point. No matter where you look, you always have some kind of limits.
And it might sound like Redigit if this guys leaves us and gets a c&d from Nintendo and he then goes and makes a sandbox game that's just as popular as minecraft/terraria and also for a Nintendo console. The ultimate conspiracy theory. (It's unlikely, though)
If he does take suggestions, he should fix the directx8 problem and upgrade that to at least a 9 or a 10, because 8 is hardly accepted and thus the program won't work for me still. So, until it's ok without having to 'copy files' and 'get directx8.dll from somewhere' and anything similar, I'll wait for the next update(s).
This is not directed to me, isn`t it?
But yes, I forgot about the c&d ... might happen again with 1.4.1. Well, sh1it happens then I guess. At least we have something right now to play with.
Can not say anything about the direct x thingy, I still have Windows 7 ...