The Mistercade does not include the 128 MB RAM or the DE-10 board.
The consolised system does not include the DE-10, but does include the RAM and basically everything in the complete stack of boards plus more. They even had somebody playing Zapper games on there, which I hope means that we will see more light gun options for the Mister in the future.
Ok, so either does not include the DE-10. But the consolized system has the ram physically integrated into the board. I hope that's not a final plan because having the ability to upgrade is vital with the advancements of cores coming down the pipe. "Snapping it out" seems like a real clunky and potentially dangerous solution. Then I'm assuming their ram board is going to be proprietary from the looks of the current one on the board. So if you need to upgrade (which could be very likely with the Saturn and PS1 core developments on the go), you'll be paying the cost of ram anyway.
Also, the add-on JAMMA board for the consolized system is only mentioned, but not seen. And probably not included in the price-point. We don't really know what features it'll host or how it will work with the consolized system. For example, power? If the JAMMA is connected will it run off the power supply of your cabinet? Or do you have run an extra power cable to plug in the adapter? I'm very skeptical that it'll run 4 amps of power through that tiny add-on port, so this could be a hassle for some people. Similar hassle to running a PC in your Cabinet... having power plugs to enter the cab, as well as having to switch on the consolized system separately from the cabinet. Also what about audio in a cabinet that doesn't have an internal amp? which is practically a majority of arcade cabinets. There is no on-board volume pot since the consolized system is running line-level audio, as opposed to the MiSTerCade where audio levels can be tweaked via a pot. That makes it much easier for cabinet owners.
The MiSTerCade is a dedicated JAMMA device, and it's purpose is to be solely that. Not a everything-in-one device.
For arcade support, not only does it have the JAMMA edge connector natively, but you also have jumper options for the extra buttons for cabinets that need button-4 on the JAMMA edge (like Neo Geo Cabs). It also has support for not only a CPS2 kick harness, but also CPS1, AND CHAMMA config as well. There is also talks about support JVS in the future, and knowing Porkshop Express, he's all about adding as much arcade support as possible.
As for the lightgun support, don't worry, the MiSTerCade will have that covered.
The price for the MiSTerCade not including the ram and de-10 is $170.00 USD. The price for the consolized system that does not include the DE-10, but does include their proprietary "snap-off" ram board is near $200 USD after the GBP exchange rate mugging. Not to mention the extra price for the JAMMA add-on board.
At the end of the day, I'd rather have something that does it's main job really well, than have a device trying to cover all bases but being mediocre at some.
YMMV.