OK. That's fair enough.
I just wonder whether people would be reticent to lay out $60 now knowing that the "finished" version is 2 years away...
This is the exact issue with early access.
The simple point is that hype and waiting sells games, it's tried and tested and unless you are a small developer who without the influx of cash won't actually finish the game, then early access is simply damaging the hype build up and has the potential to see games development cycles damaged. In particular, with the money coming before development is finished it can be a case that the real sales numbers are made well before release.
Of course subscription faces the issue that many would simply leave very quickly after getting a taste and not come back thinking "that's it". Subscription is great for MMORPGs, but for games with large single player components it just seems bizarre and unlikely to be profitable. It would be useful if it were an option for some who would then basically be paying beta testers for their new versions, but there'd need to be a system in place to make sure they're locked in, but in such a case they're basically paying their cost for each years game over time rather than in a lump sum, which just seems a pointless venture, and would make Early Access seem the more logical way to go. As already discussed though, that has it's own issues.
To me the key needs to be a solid development and release model which allows them to make sure each iteration is as good as at can get, before moving on to implementing more ambitious features to use as unit movers for the next one.
In terms of release I think they need to seriously consider a worldwide, cross platform release on all platforms, but ultimately that is up to them. I just think the key is to make a quality product, build up hype and try and build a community that knows the game and will buy each iteration as it comes. That's seems to be what they're planning too.