So, which countries do you see in Intermarium?
Ideally, Intermarium would look like this (perhaps without Albania*, and we might include Greece)...
Of course that would be Intermarium in its final stage, I'm not saying all the countries would have to join at the same time. The core is already there - V4 (Poland, Czechia, Slovakia, Hungary).
in which Poland plays dominant role
The whole point of Intermarium is not creating an alliance in which one country would play a dominant role but to unite all those countries whose very existence and independence was threatened (and very often still is - listen for example to what this maniac Aleksandr Dugin is saying) in history by their aggressive neighbours.
Poland doesn't even dominate V4, even though her population and territory is larger than other three members put together. How would Poland dominate the entire Intermarium?
I see Intermarium either as an independent alliance in case of EU breakup - then it might cooperate closely with Germany and the EU core, or in case EU survives, as an eastern regional alliance within the EU (with time Intermarium nations should gravitate towards the EU).
* for reasons of religious/cultural cohesion - West of Intermarium is Catholic, East and South Orthodox, I'm not sure if it would be entirely reasonable to bring in an overwhelmingly Muslim country into the alliance