I'm still surprised...
... that Apple, Microsoft and Google have not already bought out their own GSM networks.
For a soft SIM to be really useful, it must be fully open and, yes, let the service providers compete fairly and in a more open way.
The changing size of SIM cards is already restricting users flexibility - I don't have particularly fat fingers, but have you tried swapping micro- and nano- SIMs from one handset to another?
Plus, I previously found having a dual mini-SIM android handset really useful - one for me, one for work, so I would hope that any 'logical' SIM 'address' would allow you to have your main number/services AND your secondary/work service, with sensible seperation of services, address books etc.
The SIM card having your contact numbers used to be useful, until address books became better - and now in the cloud, so why not get rid of the 'card' itself. The GSM organisation MUST make sure that no single vendor exploits this unfairly.