If the Maemo platform is strategically important to Nokia there's no obstacle to keeping the SIM-less tablet market going for developers and customers alike. The N900's tablet functions are already battle-tested; improving its telephony functions is something Nokia engineers are doing within their secret darkrooms anyway. Yet lot of the internet and media functionality depends on 3rd party developers and generally open-source apps which are being patched up and improved from many different directions. All they need is hardware to run the current Maemo OS.
If Nokia will indeed release tablet(s) in the future then why the long gap and no information whatsoever? Wrt. price and screen size the N900 is hardly the ideal tablet developer attraction, and what hardware features should the developers target on the not-even-rumoured future Nokia tablet? Keyboard? D-pad? etc.
Being extremely phone-centric has already blindsided Nokia in a major way by the arrival of iphone and later Android and the plethora of ARM-armed touchscreen smartphones. Now they're surrendering the "companion" tablet market (and many developers) voluntarily after pioneering the platform (which, when mature, would help the S40 and Symbian sales!) and after bringing up the tablet usability from 40% to 60% to 80% currently?