1) So the reason why future updates to the styles won't work with the converter anymore is because, as I understood it, every object is going to get a secondary animation, without exception? i.e. every triggered trap is going to have some ongoing secondary animation?
Not necesserially, but rather, some objects have changes to their data file - most notably, one-way arrows - that aren't compatible with the NXP convertor's older code, which is based on the first new-formats release. If we still have the source code for the converter, it would
theoretically be possible to update it, but given how long new-formats has been out and how much time people have had to convert their packs, I'm a bit reluctant to make this kind of special effort at this point (especially given that IIRC, the convertor needs to be compiled using a much older version of Delphi than what we're using for NL nowdays) - especially if the levels can be converted using the older copy of the styles, and the post-conversion levels themself work fine on the up-to-date ones (which they do).
The issue is not with the translation table, but with the objects themself - which the converter needs to be able to load too, though I forget exactly why (EDIT: might have been to determine the correct size for resizable objects? But really, I don't remember and don't particularly care to look into it right this second, maybe later). But if you convert a pack using the older styles, then load it in NL 12.5.0 / 13.0.0 (whichever it ends up being), the level itself will work perfectly fine, assuming the usual conditions (ie: no use of now-removed features, etc - and to be 100% clear, the next update is not removing any further features, I'm simply talking about those that were removed during the old-formats to new-formats changeover). Likewise, the same applies to opening an older LVL file directly in NL or the editor - as long as those conditions apply, plus a correct translation table is present, you can still open your old levels that way.
If there's particularly huge demand for a way to convert levels to remain available, I'll look at whether I can rig up some kind of command-line mass conversion feature in NeoLemmix itself - all that would be needed here is to recognize the command line option, and mass-convert the levels according to it - NL already has support for loading old-formats levels (as well as DOS / Lemmix, (Super)Lemmini and Lemmins levels), and any level it can load it can then save back to an NXLV file. It even has support for doing this one level at a time via command line*, just not in bulk. The user would still need to put the converted levels together into a pack manually, though. But even for this, I'm going to need to hear a good reason why (a) there are packs that weren't developed for new-formats (or already converted) in the first place, especially given that new-formats has been out for a couple of years now and we've constantly reminded people that new content shouldn't be made for old versions; and (b) using the existing conversion tool with an older copy of the styles isn't feasible;
or some use cases outside of "I didn't update my pack yet" (eg. are there a significant number of Lemmini packs that there's interest in converting? That would justify implementing such a feature; it's zero extra work to support both Lemmini and older-NeoLemmix levels this way compared to supporting just one or the other).
* This feature currently exists primarily for editor use. The editor only has actual support for NXLV levels - all the other supported formats, it first asks NeoLemmix to convert to NXLV.