Yeah, it's almost certain that Themis eventually becomes our Elidibus. Makes too much sense with him having Elidibus's VA in the post-credit scenes and the mention he made about having seen us in Elpis before. Whether this is before he gains the role of Elidibus or he's presently undercover remains to be seen.
The interesting thing with Themis right now is that his hair and eye colors are remarkably similar to Venat. Given the family ties that are already going on in Pandaemonium, could it be that Themis is Venat's son?
As for Erich - the most likely scenario is that Claudien, one of the Sharlayan researchers, is a shard of of his. However, I can't shake the feeling that the mentions of Lahabrea thus far in the Pandaemonium story is a misdirect and Erich does eventually become our Lahabrea. Would be very interesting if this raid story is an origin story for both Elidibus AND Lahabrea.
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Bart, with $10,000, we'd be millionaires! We could buy all kinds of useful things like...love! ~Homer J. Simpson