- one thing that is much less powerful is cosmetic filters, which means ads may be replaced with gray squares if uBOL can't remove them entirely
- less filters overall, because the limits on how many filters are possible are pretty strict
- extension updates will be both larger and much more frequent because filter lists can no longer be updated separately from the extension
I can not give you an exact number, but it is massively bigger than the number of trackers / elements that any usable web page can realistically implement. Probably you can do several thousands database calls in less than a second due to indexing; and that can be further optimized by doing it in batches, bringing it up to tens of thousands, if not in the hundreds on modern PCs. It is literally not an issue.
I'm sure it's fast but if people want unlimited number of rules that number could start exploding.
They didn't, Google did. It is part of MV3 specs, afaik.