This looks like marketing puff. There is absolutely no content on the MGBase-T Alliance website - could this just be a PR exercise, whilst the real action happens elsewhere?
Is this just a ruse to distract people from where the real action is? There is also the NBase-T Alliance, which purports to do the same thing - deliver 2.5Gbps and 5Gbps over twisted pair. This is backed up by actual work being done at the IEEE - and was reported on by The Reg: http://www.theregister.co.uk/2014/11/11/ieee_turns_crank_on_new_wired_ethernet_standards/
Methinks the MGBase-T Alliance are bandwagon jumpers.