I think that density, limited to nobles/region, is a poor indicator. Increased competition for lordships is a good thing, as it got way too low, but what is really wanted is more nobles per realm.
Which the glaciers will do nothing about unless they provoke total realm collapses. If the border realms lose half of their regions, and can't expand to compensate, then the net result is 0 impact for most of that continent's realms and 0 increased competition for all government titles in the targeted realm. And as targeted realms tend to lose players, who find it unfair, you really end up with decreased nobles/realm ratio on that continent.
The impacts on Dwi might be different, because you've overrun half of the regions and the most populous realms, but you should be really careful about looking at density as being purely nobles/regions, without considering nobles/realm. Most of the issues brought up in the last few pages relate to nobles/realm, and have little to do with nobles/region. A realm with 40 nobles over 40 regions is just as able to secede and form new realms as one with 40 nobles over 20 regions, even if the "density" is half in the former. A realm with 15 nobles over 5 regions is not able to split up into multiple viable realms, despite having a density three times greater than the ones with 40:40, and it has nothing to do with lack of regions on the latter's part (realms can always expand).