It wouldn't be a bad idea, but to make it really viable you'd have to rebuild every existing bit of equipment with the metric fasteners! Personally, I reckon the USA adopting metric is the most insane idea imaginable! How do I know, I've been here before!
The U.K. was the first country to adopt standardised screw threads. They were called Whitworth (British Standard Whitworth or BSW to be precise!) The sizes evolved pretty naturally, so later on when finer threads were required for steel, British Standard Fine came along too! The system worked well, and you would only ever need about 5 sizes of wrench for any bolt on a vehicle!
America developed it's own standards too, but completely independently. Surprisingly, or perhaps not as they were evolving to do the same job, they were very similar. Differing only in using a thread angle of 60 degrees, and in some of the thread pitches! Wrenches however, instead of being bigger than the thread by a fixed proportion, were rounded, usually to the nearest 1/16 of an inch. This gave a greater selection of wrenches so you might now need 8 or so for the same bolt size range as the Whitworth!
After the war, it was thought that it would be a good idea if all the 'allies' used the same screw threads. The result was 'Unified' which in theory uses the best features of both the systems, but in practice is almost identical to the old American National Coarse and American National Fine. Although most folks in the U.S. refer to the bolt sizes as SAE, the threads are actually Unified!
This system was adopted by almost every industry in the U.S. and U.K. which was sensible and we are still enjoying the benefits although... every mechanic in the U.K. now needs 2 sets of wrenches!
So far so good, but in the 1980's, some numpty thought metric would be a good idea! It is, in some respects, but not in others! If you divide an inch in 2, you get 2 halves. Divide again you get 4 quarters and so on. Your first choice for a bolt smaller than an inch is a half inch, then quarter, half, three quarter and so on. There is no such natural division in metric. Half of 10mm is 5 mm, but then what? Do you adopt halves, go up in 2mm steps or what?
There are more different metric systems than inch ones, each of which uses a different range of bolt sizes. European countries tried to sort this out by adopting S.I. (System Internationale) metric, but the Germans were different, as were the French, and the Swedish even used Whitworth threads with metric heads!!
The U.K. has now adopted I.S.O. Metric. I should find nuts of 7, 8, 10, 13, 17, 19mm, and so on, on my vehicle! This is fine, but they keep jerking around with the standard, so I might find myself needing 16 and 18 instead of 17 and 19! Also, I might work on a Japanese vehicle, and they use JIS, so I might need 12 and 14 as well! In practice, I now need about 13 wrenches to cover the same range of bolt sizes that I needed about 5 Whitworth ones for!
But it doen't end there, because I still need all my SAE wrenches, and my Whitworth ones AS WELL, quite often on the same day, and sometimes even on the same job! It's a bleedin' nightmare that the USA could avoid. Unfortunately, the useless accountants who wrecked so much British industry with their 'cheaper is always better' philosophy are now trying to wreck America's industry the same way. The only reason there are metric fasteners on U.S. products is because the crappy outsourced fasteners are a few cents cheaper than inch ones! And if you have to spend hundreds of dollars on new tools they don't care!
Rant over - back to wrenching' !