I remember looking into MMX when I had this broken AiO desktop I wanted to fix: the spec is a bit vague but the mobo usually has to support the upgraded card in the BIOS too so it's not like with a desktop. I guess the rational is to stop a user from installing a card which is a higher wattage but I would have preferred if Nvidia (who designed MXM) had just made it so that a card could report 'I need 50W, 70W etc' and the BIOS would know what TPU the laptop was designed for and if the card was below that it would run.
Never got that AiO working since the parts were too expensive but the irony was it was mainly used for TV usage and the motherboard had an Intel 4500 onboard which would have handled that fine but there was no way to disable the MXM slot. I managed to find the MXM spec PDF somewhere and there is meant to be a MXM 'bypass' card but I was never able to find any. A pity.