Not sure if it's relevant but from what I can tell DMM always brings back these "limited edition" characters anyway and sometimes even permanently after about a year.
From what I can tell on FKG all the limited characters that were once only reserved for Halloween, Christmas, Summer, etc eventually become part of the permanent gacha.
All Limited SSR Kami return after 1 year WITH the new batch but ONLY THE NEW are Buffed. Best chance to get the SSR you want is ALWAYS during the release. If you do not plan to whale best is to reroll till you get them. Sol *Any form* is still the top healer for some weird unknown reason. Unless NA is changing the stats or abilities (which they haven't so far) she is still a great Kami to get. The only one close to her is X-mas but that is next year since we didn't get the first set of X-mas chara last year (due this year)
Hope this helps.
Magicami Starter Guide: Rerolling for Success
Rerolling in Kamihime Project: How to get FREE SSR Kamihime
Sanahtlig's Kamihime Project Toolbox: Includes damage calculators and other useful tools, data, and info I've designed and collected. Make a copy to edit.
Would still try 2 get summa Bryn chan since she is da only light healer