The other day, another Trainer and I were comparing our platinum medal progresses, and as can be predicted, we have mutually exclusive progressions - I have ones the other doesn't and the other has what I don't, including for partials toward platinum medals. In a way, our focuses are different due to our conditions, so we're chasing after (and thus have) different medals accordingly. Some commonalities were also evident, though, and that's something that other Trainers can also consider to take advantage of.
For that, it is likely that many Trainers will have a significant progress on their type medals for catching specific types, and they can take advantage of them to elevate them to the platinum level. The regularly occurring Community Day as well as the frequently occurring thematic events can be used for this purpose, particularly for the specific medals that aren't already at the platinum level. Some amount of time is also still needed - for most things don't happen in an instant - but they can and will get there.
Meanwhile, for the medals that involve specific objectives, the most sensible effort would certainly be to finish the ones that are closest to completion (region Dex medals could be a contender) and start chipping in effort for longer-term medals (like the Rising Star Duo and Ace Trainer medals) - all of these based on the comparison as above. By the time Level 70 and up comes about, the efforts can then be directed to the other tasks, and the platinum medal task won't be a burden.
It's a given that those who are serious and/or routine about Pokémon Go will think about the upper levels and how to approach them as they approach them. That has been true in the Level 50 past and now again after the level cap change, which resulted in the addition of tasks concerning platinum medals in order to level up in the "final stretch". The result is a chase for those platinum medals - whether they're already in the thick of it or approaching it - and sensible efforts will likely be needed as the chases begin or continue.
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