Yes,
If you use a single html file, it is loaded into browser memory, so 1GB is likely unusable. There are ways to compress text for search algorithms but I do not think this relevant here. You could look into node and bob solutions for tiddlywiki, and what we call skinny tiddlers, but I suspect this will impact the searchability.
We cant easily say what the maximum size of a tiddlywiki.html is because there are more than one way that it can get too big, browser and device limitations can also impact it.
Can I suggest you review the original idea for this project and tell us about it. We may be able to give better advice if we know what you are trying to achive.
Regards
Tones