Well, if its possible while playing sound openings, then why
not? For personal amusement/ curiosity mostly

So much choice and whims like that are probably as sane a way to do it as anything else.
Ok, so a terrible idea if you're learning and have got put off by one bad experience or something. If you know what you're doing though, entirely sane.
I actually find it interesting to observe that you
can build a fully sane repitoire where you'll normally get French pawn chains but will very rarely go f6 before move 10-15, and not that often afterwards.
I don't think you can do the same with c5. f6 clearly isn't as fundamental to blacks play.
I'd add things like 3.. a6/h6 vs the Tarrasch ^ Ngf3 Nf6, g5 etc and the 7.. Kf8 Winaver/McCutheon to that list you had above. Probably the 7.. Nf5 Winaver too. Various slightly older treatments of the positional winavers.