What is likely to break on my R1100?
First and foremost: follow the maintenance schedule. It covers a number of items that most owners will ignore during DIY maintenance, such as the throttle cables and alternator belt. Items that are on the maintenance schedule cannot be considered failed if they break after having been on the bike longer than intended. Throttle cables can probably stay in for a lot longer than the specified 24k miles, though.
Aside from the 'wear items,' though, you may experience the failure of the rear drive bearings and the ignition timing sensor (Hall-effect sensor) at about 100k miles. Ridden normally, the clutch should last well past 100k miles. Paralever pivot bearings only last about 40k miles. Speedometer cables can break, especially if they have nicks in the plastic coating, around 75k. Cam chain tensioner rails can break, usually well beyond 100k miles, and they are quite difficult to replace. Swingarm and Telelever bearings seem to last forever.
What about splines?
The relatively few spline problems on the Oilheads seem to be from manufacturing or assembly defects. There is no specified maintenance on the clutch spline and they don't seem to need cleaning or lubrication for about 100k miles. As far as a lubricant, BMW has released a new grease specifically for clutch splines, but it seems to be very thin and many mechanics avoid it. The best alternatives right now seem to be Honda Moly 60 and Wurth SIG-3000.