Are you sure that this (playing only as white and not accepting challenges from good players) is so common that it needs to be done something about?
Or is it maybe only 1 or 2 players who do that?
None of the top10 (or lower) Five-in-line players has declined an invitation (2-game matches) from me so far. This was also true when I just started playing here and was still unrated.
And one thing: I think you have seen this problem with Pente which is a new game here and so the BKRs are based on relatively few games. As the number of played games increases the BKR becomes a much better indication of the players skill than after a few games only. For example, I`d imagine after 50 or so played games Dmitri will have a BKR in the neigbourhood of 2500 points AND can still keep on increasing it. A not-so-good player may be able to get a good rating in the beginning BUT is bound to lose a few games at some point AND can never climb back up. To do so he would have to play against good opponents, who probably wouldn`t agree to play only as black.
This is because after you have reached a high BKR getting points gets really difficult and you have to play good opponents to get ANY points at all. For example, if I win a Five-in-line game against an opponent who has BKR as good as 2100 my BKR increases with a whole 1 point.
Shortly: provisional BKRs are often misleading, when you get an established BKR it is already much more reliable and the more you play the better indication of your skill it gets.
Top10 (or so) tournaments might actually be a good idea, BUT to be REQUIRED to play in a certain tournament is not.