From my mulling and talking with people and getting the convergent point of various descriptions, this is my discovery:
One big hole between MBTI and Socionics is the difference between Se and Si. First of all, forget about MBTI functions. MBTI DOES NOT USE FUNCTIONS! Socionics do that. So, with that moved out of the way, here is something to ponder about(the more you think, the more visible it'll get!):
Some say that it should be compared like this:
SEE = ESFP
ESI = ISFP
ESE = ESFJ
SEI = ISFJ
But if you actually stop for a moment and think about it, how about this:
SEE = ESFJ
ESI = ISFJ
ESE = ESFP
SEI = ISFP
This could be further proven by static / dynamic reinin(do ESFPs seem static lol? How about ESFJs? ).
Really, the whole MBTI spectrum is phased when compared to Socionics spectrum due to Myers doing fun things with introverts and shift in Se and Si in socio. This shift is what reconcilles everything. Just something to think about...
edit: this could possibly be applied only to S types. But still, it's one huge hurdle less!