I think the main goal is not to simply collect national imagery, but to discuss what universal heraldic elements could be accepted by most Slavic nationalists. For example, white-blue-red palette is common for almost all Slavic flags (except Ukrainian - this unfortunate nation borrowed yellow and blue from Swedish flag).

In contrast, double-headed eagle may be less acceptable, because for Poles and Czech this could remind unpleasant times when they were under Imperial control of Russia and Austria.

Then, what about the cross? Catholic four-point cross +- would be definitely unacceptable to Orthodox Slavs, because they have elaborated theology of eight-point cross +|-/- symbolism, and vice versa. I also think that we must reject any pagan symbols.

Perhaps, it would be nice if all the participants would send their national imagery to Wojtek and he would place the images on his web page, so participants would be able to discuss the topic more productively.