The 13" Envy has an average review of 4.8 stars compared to the 15" average review of 4 stars. Not only that, the 15" Envy is $200 cheaper base configuration than the 13" Envy.
I seriously doubt the next 15" MBP will have ATI 5830 graphics, nor include 1GB dedicated video RAM, nor have an option to 16GB RAM (because probably no 45W CPU), no Quad Core CPU, no dual drive configuration from Apple, no 3 USB ports, nor an eSATA port, nor an HDMI port, nor 1920x1080 HD display option, and DEFINITELY NO BLU-RAY!
It's an awful lot of compromise to be "stuck" with a MacBook Pro, isn't it? This is everyone's dream MBP, and it's too bad Apple will not give it to Apple Mac lovers. MBP buyers would gladly pay for every one of those options to get a MBP with the power and performance of the Envy. It's too bad that Apple doesn't really have a lot of BTO options to allow MBP buyers to configure the MBP they really want even if the costs are ridiculously high.
This is another one of those replies I KNOW I'm going to get flamed to death for by spec nerds but... no, that's not everyone's dream MBP, at least it's certainly not mine. Uber fast graphics and 1Gb of memory, quad core CPU and dual drive configurations eat battery life and generate vast amounts of heat. I would prefer to have a slightly more sane spec, a laptop that doesn't roast your dinner for you and a battery life that at least has a shot of lasting for a few hours away from the mains. I'm not even sure that the MBP's thermal envelope would be able to cope with the heat even if you could buy all that on BTO.
USB 3.0 would be nice for future proofing but that really is very very new. Esata is kinda pointless if you've got USB 3 and while I've seen hundreds of laptops with HDMI ports I don't think I've ever actually seen one being used to feed a TV. Higher res screens might be a nice build to order for some people but I'd never want a 1920 screen on a 15" laptop, it'd give me a headache within minutes.
See here's the thing: laptop design is always about compromise. The Envy 15 review on Gizmodo came in at less than two hours battery life and the Engadget review reported serious heat issues. A MBP packs in more than enough power for the VAST majority of users while not loosing sight of the need to be more than a geek's wet dream. When I bought my 17" MBP back in the summer of 07 I knew I was paying more than I would do for the same-spec machine from a PC manufacturer. But there was no other machine on the market that offered the same blend of performance and portability. It's the same story today, the MBP may be beaten on performance by stuff like the Envy but it remains the best all-round compromise if you don't mind spending the money for it.