Good point, but I still think that shift and symbols are quite a different kind of modifiers to merge them on one button. Shift just changes letters case while symbols turns on sublayout with totally different charset (so it's not a modifier actually).
I've found two kinds of virtual keyboards: with (for example http://goo.gl/B946t6) and without (http://goo.gl/LbwHGC) symbols switch. The first kind used when there is no much space to place digits and symbols with letters (that's our case), and the second one uses shift as the symbols switch for digits row.
We could add more symbols sets in the future (e.g. smiles or whatever) and use cycling for "symbols" button. But "true" modifiers should be represented as standalone buttons I think.