There are four existing zones that are already on permanent UTC-7:
America/Dawson_Creek
America/Creston
America/Fort_Nelson
America/Phoenix
None of these zones makes use the DST bit. The time zone is displayed year round as MST instead of PDT. I don't think anybody complains about it.
I don't see any compelling reason to treat the two Yukon zones (America/Whitehorse & America/Dawson) any differently than the four existing UTC-7 zones.
A good point. I had forgotten about the smaller areas already observing -07 year-round.
So, this new proposed patch, attached, affects abbreviations from this coming weekend. But timestamps remain unaffected until November.