The battery will be obsolete compared to what's out there.
1) Until then you have use of the features provided already, and what is added up until then. Pricing is ballpark inline with general automobile tech feature pricing, and very likely on par or better if others provided directly comparable features. About as close as it gets right now to a comparison is $5600 to add Super Cruise to a specific Cadillac model, and that is still pretty shaky comparison given it is very whitelist limited and such.
2) Regardless of whatever other battery is potentially available, 250 miles is still 250 miles (or wherever you pack is down to), and the utility of that is only going to increase as charger infrastructure continues to build out.
3) A battery pack swap/refurb is almost certainly going not going to affect the FSD option. Boom, another several hundred thousand miles life on your vehicle.
#2 does mean it is going to make more sense with LR vs SR or the LEMR, and whether or not you're personally in the market matters. Potentially #3, as well, as I'd expect pack upgrades to come to the larger vehicles first. They have the drive units to better make use of the better performance characteristics we'll see out of future batteries.
There is always the question of whether you care about the features, if there is value there for you (and if you have the $ on hand to acquire that value). But that's a different thing.
P.S. I would be entirely unsurprised to see Tesla add a subscription option for FSD at some point. But they've been slow on the lease front, too, so not sure Musk has got in his mind yet that he's willing to swap a pretty good cash up front stream (maybe 30% of vehicles sold adding the option) for the incremental extra overall sales but the cash coming in on delay. Cash up front maybe isn't as critical as it once was for Tesla but, especially given CoVid-19 production shutdown, it still matters a lot to them. They've got a lot of expansion plans that need capital.