A Lifestyle+Downtime small supplement would be nice. On the other hand, given the amount of agression thrown around at 'hey here's some training time guidelines, but do whatever feels right for your campaign', having 'hey here's some downtime guidelines, but do whatever feels right for your campaign' might also get massively attacked and be considered a risk.
There's a big difference between having something like that in a core rulebook and having it in a splatbook or alternate rulebook. I think SR's always had some issues with loose wording on rules, as well as identifying RAI vs RAW.
The SRM guidelines are clear and use direct sentences. For example:
"Gear
must be fenced through one of your contacts per the rules on Fencing Gear (SR6 pg. 246). However, the percentage increase from an Influence + Charisma check
is capped by Loyalty, which
is effectively
reduced by one for every point of Heat."
There is no room for doubt here; if I were editing, the only change I'd make is getting rid of that pesky adverb. It also provides a clear reference to a rule (Rules on Fencing Gear), and the book + page number where to find that rule.
Sometimes, it is okay to be more nebulous. From the CRB, pg. 36:
"A glitch on a roll by a helper
should cause significant distraction to the next action or few actions they take, preventing them from gaining or spending Edge for one to three combat rounds."
The 'should' used here is fine because glitches tend towards the realm of GM fiat: that is to say, the rules cannot account for every situation, so they instead provide intent and a recommendation. The direction is clear- glitches cause some sort of significant distraction. The specifics are left to the GM, since "distraction" means something different in different scenarios.
Compare to this:
"The time it takes to raise any given ability is
truly only suggested—the actual time used is up to the gamemaster, with times best fitting the story they want to tell, but we offer the listed times to create a
general consensus."
First of all, get rid of that adverb. "Truly" adds nothing. Second of all, this does not provide a clear enough direction for the GM with "best fitting the story." When you write a rulebook, you need to write it as if it's the first board game that someone's played. Failing that, write it as if it's their first RPG. SR isn't the only TTRPG guilty of this. I digress. If, later on in the GM section, they talked about having "fast-paced" versus "long" campaigns, and suggested that GMs alter training time to better match the pace of runs, this would be acceptable. As it stands, the rules do not provide enough direction.
It's further muddied by "general consensus." Some RPG players might argue that rules themselves are a "consensus." If it said "we offer the listed times as a baseline," that gives the GM an idea that they can make it slower or faster. If they said "but the listed times will work for most campaigns," then you get the idea that the times are the standard.