But, that's the point here. You can already do that. 1 level of rogue and POOF you have multiple skills with expertise. Getting expertise in Althletics is already very, very easily achievable.
Has it been a problem? Are people constantly sending Agony Aunt style letters to WotC complaining about how grappling and expertise is broken? Three years of 5e on these boards, and I'm not recalling a single instance of anyone complaining about this.
So, gaining Expertise through a feat is about the same cost as taking 1 level in rogue (after all, you gain quite a suite of goodies with 1 level of rogue) and fits a LOT better with many character concepts where a level in rogue makes no sense.
The mechanical arguments here don't make any sense to me. We've HAD this for three years already and it hasn't been a problem. Why is it suddenly a problem now? Up to, what 9th level (Books are not here), we're talking a +3 bonus to a single skill. Even at 20th level, we're talking a +5 bonus. That's it.
If your game breaks because someone has a +5 to a skill, I'm thinking that there might just be larger problems at the table.