MacMini is strongly rumored to be upadted in August, after the release of Lion OS in July. You can bet new hardware will only be available after the release of the new OS iwch is due soon. Its also strongly rumored that Macmini will be updated along MacPro, and that macbook air will be updated along the release of Lion in July.
The updates are rumored to be: Sandy bridge and thunderbolt. When this happens, all mac line of products will have been updated to Sandy bridge and have thunderbolts conncectors, except for white macboook. Therefore is logical to assume that with the release of macbook air, Steve will give some adress to white macbook, either discontinuing it, or updating it as well.
Personnaly, I hope Apple will update the white macbook, Im getting one!