First of all, with regard to non-WAAS G1000, Garmin did not say they had no more GIA-63W units. They said they would not make them anymore. They are in stock. The upgrade kit is in stock at Garmin. I just bought one this month. Second with regard to the NXi upgrade, I think it will happen, but it will be a while. If you look at Garmin's project list, they are going from King Air down. The first SE they are doing is the PA-46. I suspect Mooney will be one of the last. Starting with the higher priced machines makes sense. I suspect it will be long enough that a WAAS upgrade to a legacy G1000 is worthwhile.
If you don't upgrade to WAAS however it is not a big deal. Yeah you can't do an LPV approach. Look at the approach charts for most GPS approaches. The difference between an LNAV and an LPV in most, not all, but most is 100'. How often has that made a difference to you? I suspect unless you are in a scheduled operation, rarely. I can even show you an approach where the LNAV minimum is lower than the LPV (KMTN RWY 33). Second restriction is not be able to file to a GPS destination AND alternate. Again, how often does that raise its ugly head? Depends on your home base. Me, a little more but not a lot. My issue is the way my home airport is laid out, people hit the GS antenna a lot so you have to the LPV to get really low.
As to the Bravo, like the machine but it is different, requires a thorough understanding of its operation and it is a tad thirsty which is why I opted for a normally aspirated Continental. If you get a good price, you can buy a fair amount of fuel and accounting for present value of money, may be a good buy.