I'm not sure of the degree of the core re-write but there have been many wishes for the likes of non modal, live reports, less clickiness etc which have been around a long time but I don't see any of those as big selling points. Whilst RM7 has many niggly little shortcomings which could easily be overcome, imo, I have got to know and trust it, maybe that's the master plan to encourage me to upgrade.
Therefore I am in no rush to see RM8, but cash flow might disctate otherwise. I pushed hard for the release of RM4 and that became a disaster, I don't take responsibility for the disaster as it was being teased for nine months before release, it simply should have been tested more thoroughly. Anyway it was not a launch RM would wish repeat so as long as steady quality programming is going on I am happy to wait, it will be interesting to see what the hooks for existing users to upgrade will be.