I can recommend BeepStreet Sunrizer (inspired by the JP80x0), Waldorf Nave (Wavetable synthesis), Arturia iMini (Moog emulation) and Korg iMS20 (MS-20).
Less fussed by Arturia iSEM (Oberheim SEM), although this is probably a taste thing.
Not fussed by Korg iElectribe or Korg Gadget, although not fully explored the latter yet.
Purchased an IK Multimedia iRig Pro when it was on offer to get MIDI from my keyboards into the iPad, also allows you to inject audio into it via a combi ΒΌ" TRS/XLR jack such as a guitar or mic for mobile Amplitube fx or sampling or whatever. Even has phantom power (supplied by battery) for active mic duties if necessary.
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PS > And another thing! Will the Ti|3 have user customisable/importable wavetables?
A ribbon-controller or XY-Pad might be nice, too, please! Thanks!