Rank lock is a nice idea, but it will definitely lead to rank inflation. For example, if you want to try out new/fun decks, you’d lock your own rank. Fun deck and new deck are, in most cases, less competitive than “standard” decks. If a person without Rank lock matches with you, with your rank locked, the opponent would have an easy time beating you and thus gain rank faster. Therefore I don’t think your idea of Rank Lock is feasible.
Suggesting that Rank Lockers should have a different queue is the same as suggesting an unranked queue. In most games, queues match people by comparing either their explicit ranks (like Bronze/Silver/Gold/Dia… in Duelyst) or implicit ranks. Nearly ALL games uses implicit ranks (Match Making Point, look into competitive chess matchmaking for more details) for normal queues. Theoretically, your relative explicit rank should be the same as your relative implicit rank, i.e. balance should be good as usual.
(Winning Streaks yielding bonus increase in rank could cause rank inflation and thus the discrepancy between explicit and implicit ranks, but that’s not the main concern of the current topic.)
I reckon that the absence of non-ranked queues is due to the small player base of this game. I remember this claim (and this topic on a whole) being echoed in the forum numerous times.
Responding to OP, I’d say that don’t care too much about the rank unless you’re about to get up 1 division. You can’t fall below a division: say you’re gold 8, the lowest you could go is gold 10. Also, the highest rank you achieve within the season is recorded, but not your rank at season-ends: say you’re gold 8, and you fall to gold 10, your own profile and season-end rewards will say that you’re a rank 8 instead of rank 10. Personally, I seldom care about losing ranks, because from my experience (a typical Diamond 5 dweller), a random deck could get you through Silver, and a semi-decent deck should be enough for you to go past Gold. Just have fun and enjoy the game, and be easy with your rank statuses.