Jack_M
To be honest i hoped it would be a much, much smaller chip + minimal circuit that was going to replace the PKOB

 
If you want small, you may want to try mine. We sell pre-programmed PIC16F1454 chips which you can simply solder on your board. Apart from the chip, you only need few resistors and 0.1uF decoupling cap. You cannot get any smaller than this. It can program over 1,500 different PICs, works much faster than PICkit4, and also provides UART interface to the PIC:
 
http://www.northernsoftware.com/nsdsp/brd/
 

Other than an even more cut-down version of the PICKit4; i fail to see the point of the Snap. not being able to power ANY target is just silly,LVP only is a major limitation,not just for PIC's but definately for any AVR parts.
The PICKit4, incidentally, has a 'green-light' coverage of just 5% of Microchips part range, according to the latest release notes; around 130 out of almost 2500...so much for the 'Production Programmer' it was touted as when i bought it...after three revisions of MPLAB-X it still beta all the way.
The little 'pay-per-feature' hinted at for the PK4 is a bad sign too; microchip are obviously confusing development tools with video games, and trying to upsell to 'unlock' exta features.This gives a real insight into the current mindset at microchip...are we paying for false promises,toys, or development tools? i really don't know any more.

- Absence of target voltage is a concern, but as others noted it's on par with many of the tools from the competition
- LVP only is not really a limitation, unless you use only > 10yo parts, in which case the chinese clones of old tools are widely available for less than what microchip asks for the snap.
- PK4/ICD4 part coverage is sure a concern, but as larry hinted this is probably due to how they decided to re-do the programmers from scratch. There are a load of parts that need testing. best you can do is drop a line to microchip and ask for them to add support for the parts you need, so they know what to do next. I did it with my personal gmail account, i got promptly answered and in the following release of X all the parts were at least yellow (not all members of family, only the specific parts i requested) some even green.
- pay per feature is a concern BUT somebody up here suggested it refers to remote usb debugging and some other things that are already a paid addon