This is somewhat based on opinion, but I really think lower tiers would be better off returning to the 3-month-only tier shifts and discarding the quick shifts happening every month right now. Either with the release of Sun/Moon, or now.
Back in November/December 2014 during the time just after ORAS had came out, there were problems with usage stats missing and not reflecting the current metagame. So at that time, rather than ignore shifting, a different cut-off was used to shift pokemon based on a single month of usage rather than three. Fair enough, that was special and not a big deal. During 2015 though, this was kept in place to allow for Pokemon to quicker shift down to the metagames where they are "supposed" to be in, and means tiers may shift every single month rather than once every three months.
After nearly half a generation of doing this, and for the full lifetime of a game (it will be nearly two years, if you're wondering) I'm not convinced this is something that should be kept in place. First of all, and perhaps most importantly, this has kept every non-OU tier in a constant state of change with only very short periods of time between every change. Tiers barely get a chance to settle down before new pokemon enter, or staples leaves and the metagame changes again. Constant changes doesn't lend itself to properly allow a tier to explore options and develop, and as a result they will have to develop far slower, or not at all. Three months give a much bigger window for a tier to settle down, develop, and reveal eventual suspects, without risking a new pokemon dropping midway through a suspect test and making it essentially an entirely different metagame than the suspect started in (this has happened before).
One of the big counterarguments I've gotten from this is that it prevents a tier from being stale and keeps the tier fresh. This is purely opinion and there's no proof that the tier wouldn't develop and change either way, even if you didn't introduce new pokemon to it every month. Furthermore, cases like Mawile/Pinsir doesn't exist anymore either, as Megas and their base formes are tiered separately now so this doesn't impact any eventual bans of those anymore.
So yeah, I don't think the quick shifts were a healthy addition to tiering and I'd like to see them retired for Sun & Moon (or now).
Back in November/December 2014 during the time just after ORAS had came out, there were problems with usage stats missing and not reflecting the current metagame. So at that time, rather than ignore shifting, a different cut-off was used to shift pokemon based on a single month of usage rather than three. Fair enough, that was special and not a big deal. During 2015 though, this was kept in place to allow for Pokemon to quicker shift down to the metagames where they are "supposed" to be in, and means tiers may shift every single month rather than once every three months.
After nearly half a generation of doing this, and for the full lifetime of a game (it will be nearly two years, if you're wondering) I'm not convinced this is something that should be kept in place. First of all, and perhaps most importantly, this has kept every non-OU tier in a constant state of change with only very short periods of time between every change. Tiers barely get a chance to settle down before new pokemon enter, or staples leaves and the metagame changes again. Constant changes doesn't lend itself to properly allow a tier to explore options and develop, and as a result they will have to develop far slower, or not at all. Three months give a much bigger window for a tier to settle down, develop, and reveal eventual suspects, without risking a new pokemon dropping midway through a suspect test and making it essentially an entirely different metagame than the suspect started in (this has happened before).
One of the big counterarguments I've gotten from this is that it prevents a tier from being stale and keeps the tier fresh. This is purely opinion and there's no proof that the tier wouldn't develop and change either way, even if you didn't introduce new pokemon to it every month. Furthermore, cases like Mawile/Pinsir doesn't exist anymore either, as Megas and their base formes are tiered separately now so this doesn't impact any eventual bans of those anymore.
So yeah, I don't think the quick shifts were a healthy addition to tiering and I'd like to see them retired for Sun & Moon (or now).