I understand the frustrations but the problem with mass storage is that it surrenders all control of the internal storage to a PC not a problem when that's a different chip but on the n7 and most new smartphones its an emulated partition and giving over total control would mean that android cannot function at the same time. This was brought in to stop manufacturers using two separate chips giving you loads of "storage space" but very little application space. Its a work in progress and has many issues but its here to stay I don't think any ROMs will support USBMS as it not possible on a single chip without shutting down android.
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Programming is a race between engineers striving to build bigger and better idiot-proof programs, and the Universe trying to produce bigger and better idiots. So far, the Universe is winning