After Prague you could go to Poland - Katowice, Krakow, Warszawa, Gdansk, maybe Malbork. Then take a ferry from Gdynia to Sweden.

The obvious choice, avoiding ferries) is back to Berlin (maybe via Dresden) then Hamburg to Copenhagen to Gothenburg and onward to Stockholm.

Without giving any hint what you like this is just some of touristy/wiki/´the best 10´ etc-listings:

Salzburg, the sound of music

Innsbruck, Tirol, house with golden roof (well, just as I was there yesterday)

Scenic route via Austria inland lines: Bischofshofen-Schwarzach-then north till Linz-connect to Ceske Bud-CZ

CZ; Ceske Budejovice and Cesky Krumlov (though recent notes many trains bustituted and problems)

Area N-E of Praha, CZ/PL border land, around Liberec, mountainous (not all raillines take passes, but dirt cheap compared to SL or Skane)

Mac-Pommes, the german nickname for Mecklenburg/East Sea coastal area, the afterdays of summer, several old-style seaside places like Binz, Stralsund, 

As you likely know-esp. for the anti-alco Scandinavikser; CZ, PL and DE have very good and dirt cheap beer (still from 29 ct=trekroner for ½ ltr , CZ and PL without pant)

Nattoget SJ fra Hamburg har bare liggeplasser for now, sommer-only DSB seats only Nattoget Hamburg-K/obenhavn gar ikke. (as I took it last week). or use snälltaget_ DD=Dresden/Berlin-Hamburg