EMIB is nothing like infinity, EMIB is akin to the silicon interposer that AMD use on Fury/Vega. Also the EMIB is ONLY used between the AMD gpu and the HBM2, the CPU is separated and connected over organic packaging.
Infinity fabric can be used over a silicon interposer, over organic packaging, over pci-e, over HT, over anything, it's the method of communication signalling, it's the processing and handling before sending it over literally any connection of any type. EMIB is a connection, it's nothing to do with signalling.
In effect, from what I understand, rather than with interposers having all the TSVs inside the chips themselves then connecting with one basic layer of copper connections in a cheap as chips interposer, it's basically taking 'normal' chips and sticking all the complex stuff at a higher level in the EMIB chip and Intel claim this is way cheaper but there is little to no evidence of this in the real world. Silicon interposers are dirt cheap because they can be made on older process nodes so can be made in cheaper fabs which don't have a huge demand on them anyway and they are just a few metal layers rather so take a very very small fraction of the time to process that a normal wafer does. If a normal 40nm wafer now costs along the lines of say $2000 to process taking 4 weeks, a interposer wafer probably costs $200 and getting 80-100 interposers off it even for chips like a Vega. Compared to what probably costs $0.5 for an organic interposer it's 'expensive' because it costs 300% more, but it's still only $2 and allows a large reduction in power.
EMIB uses smaller interposers but also makes them more complicated and requires sticking more of the die to die interconnect in a smaller area, this isn't usually a problem, most of the infinity connections in Zen are at the edges anyway, though that is partly because it uses organic packaging, if it used a full interposer maybe the connections die to die would be more direct, more numerous and offer lower latency as rather than going through one main line to each die, almost every part of every die could have a direct connection. That is the cost, EMIB is in effect, a baby interposer, but when an interposer has overall very small costs it's a pretty pointless inbetween step anyway. As shown, you can achieve pretty similar to EMIB at an organic packaging level as AMD have done with Ryzen.
EDIT:- Also to point out, EMIB has been talked about for a couple of years at least, hence when people were saying Intel don't have anything like infinity yet, they already knew about EMIB. Again in reality, a full interposer is realistically more advanced and offers the ability to make far larger number of die to die connections.