Not that I would of course (internal chip kicking in there)

I would build an application platform which gave the following:

• Easy customisation so ISVs could verticalise an application quickly and simply
• No weird tools, just familiar MS-type stuff and a nice Web UI to do the normal things (create and customise Workflow Foundation workflows, customise entities, create 1:n, m:n relationships, that kind of thing).  Actually, if you want to create and customise workflows using Visual Studio I'll throw a few extra helper tools in as well.
• Multi-tenancy, multi-lingual, multi-currency. 
• Multi-coloured, multi-pack, multitudinous (great word, not as good as 'thrashing' but still good)
• An Asynchronous Services cluster to run Workflow Foundation components and asynchronous plug-ins
• A simple, open and dynamic Web Services API, very important in this modern day of the interweb and computers connected by wires and things
• A very nice web UI-based Report Wizard that even Basil could use
• Off-line cached SSRS reports out of the box, yes, they'd like that
• In fact, while I'm there, off-line web service exposure, off-line data synchronisation and, what the hell, off-line .NET plug-ins

And a few more things that'll come to me.

No-one will think of this - I'm off while it's still fresh