The problem with retro shows is that a lot of them are shot in 4:3 480i (SDTV) format which is not suitable for HDTV.
Some of the 1970s/1980s stuff that was shot on video - sure. But a lot of earlier stuff, and even a fare amount of 1970s/1980s material was shot on film.
I took a peek at some of the CHCH programming - and Lost in Space, Mission Impossible, Hogans Heros, and I Love Lucy all looked superb, and were clearly recent 4:3 HD transfers! Far better picture than in the 1950s and 1960s. Two or three of those are surely the same stock of stuff that CBS All Access is showing. As is The Twilight Zone I assume, which looks fantastic on Space currently as B&W 4:3!
Coincidentally, I noticed M*A*S*H broadcasting around midnight on TLN and to my surprise, it was a 16:9 HD image. (I'm not sure how CHCH is broadcasting it). History was broadcasting it until relatively recently, and I'm pretty sure they were 4:3 SD transfers, from the odd episode or two I watched a bit of.
I dug a little, and apparently the 16:9 HD transfers for M*A*S*H first appeared on Hulu in the USA earlier this year.
I know some people despise 16:9 versions of 4:3 programs - but to be honest, M*A*S*H looked superb last night. They haven't just trimmed the top and bottom, but they've gone back to the originals and rescanned, picking up more material on the sides, and also reframing it, so sometimes they pick up more on the bottom, and sometimes they pick up more on the top. So it doesn't look unnaturally zoomed in - at least to my eyes.
If it's done properly, I'm quite fine with it. The Star Trek TOS episodes that Space aired a couple of years ago (perhaps they still do) were also 16:9 versions, and I thought looked pretty good too.
And if it brings in more viewers - why not. Purists can surely find VHS copies of the scratchy originals, where all the colours have started to fade, if they want to relive just how bad 1970s picture quality was.