alternativess to Stelviio Pass
 

If Stelvio Pass is still closed next Wednesday, what is the most interesting route from Lake Como to Salzburg for a motorcycle?

At this time of year it is much more a question of what routes are open.
The Grossglockner was still closed last time I looked and many other routes will still be under snow.

The logical route to traverse the Eastern Alps (you have the whole of them to play with) has to be those roads that the highway authorities keep clear of snow and ice for the traffic.

The Stelvio doesn't look like it's opening any time soon from the webcam pic. I'm sure you've considered the obvious route which is down to Milan, over to Verona and then the Brenner pass to Innsbruck. It does fail your "interesting" condition but at least you'll get there.

Many of the better riding routes may well still be snowbound but you can check their current status via the links on the Alpine Roads site - AlpineRoads: Pass Conditions

You have options in a northward direction such as Reschen Pass (to view the submerged church in a dam with the steeple acting as a periscope) or Foscagno Pass (from Tirano) then Livigno and north through some pleasant roads.

Alternatively, make your way east toward Lake Garda and then north through Madonna di Campiglio then Brenner, similar to the suggestion below. The weather in Innsbruck is currently 25C and while changeable tomorrow, should hit highs of 20C+ for the next week. Most of the snow here in Innsbruck has now melted and local passes are all open.

Try this website for a list of the passes and their status:
ALPENP�SSE.CO | Stra�enbericht Alpenp�sse und Bergstra�en | Wintersperre