If there is a new processor board designed for this to use a more powerful processor and other capabilities beyond an arduino I strongly suggest the Freescale i.mx6 line of processors. There are lots of fully functional development boards with LOTS of features, enough to make a full blown PC with. These are used as the brains for many vehicle navigation systems and have automotive stuff built in. Such as 2 CANBUS ports
Technically you could build a breakout board that would connect to a M2 interface board right now and connect to a Freescale board and make it fully functional within a short period of time. You would have a larger board than an Arduino for sure but would be able to run something such as Linux, Win 10 RT, QNX or android.
If built from scratch you could easily build a high performance setup using an i.mx6 chip and build into it support for whatever can fit on board. Even have room to put maybe 2 short PCIE ports onboard so you could support Wifi/BT and cellular or whatever right from the system.
Software development on such a system would likely be much shorter than on the Arduino since most of it is already done and well integrated. But it will be a bigger dongle and might take up more energy although the i.mx6 is designed to run in an ultra low power mode too.
Here is one site with developer boards of different configurations.
I actually own a couple of the following boards but don’t currently have the time to consider doing anything with it like this. This board only has one canbus port but has the I2C, SPI and some GPIO stuff on board and sufficient for trying to get it running with the M2 interface board.