I wouldn't buy one now with the idea you might want one in the future.

I think the issue will be generic vs proprietary parts. There will be special battery packs/mounts that might be maintained for a decade, then just go away.

You may be able to rebuild an old battery pack with new batteries, or fit an auxiliary battery into a rear trunk bag. But, may not be able to get "vintage" OEM battery packs in the future.

As with everything, the E-Bikes will depreciate. Drop $4K now, and in a couple of years (or weeks), you'll have a $2K bike. And, in a few more years, a $1K bike, and a bit longer, a $500 bike, and wait more, and you'll have troubles giving the thing away.

Buy the bike & technology that you need today.