3G Network Sharing: How To Isolate Performance Issues Between Operators

Broadband Expert reports that 3UK and T-Mobile UK are making progress with their joint 3G radio access network and that Ericsson will manage the venture. There are different approaches of network sharing like one company covers one area while the other covers another. This approach however, sounds like one organization maintains the RAN which is then used by both mobile operators. In this scenario, I wonder how both companies will ensure that the amount of traffic and behavior of one core network does not impact the performance for customers of the other!? How will the bandwidth be shared in practice over the same base station? 3UK for example has a notoriously bad performance record and I wonder how T-Mobile will isolate itself from those issues once they start using the same base stations. I guess each company using it's own carrier(s) on a base station is probably a way to ensure this. Here's a link to 3GPP TR 22.591 which gives an overview of the available options. I wonder which ones T-Mobile and 3UK will implement with their common RAN. Also, it would be quite interesting to know if the two companies will share the RAN everywhere or just in rural areas. 5000 base stations are to be decomissioned. But where? And finally, what will happen if one company would like to densify the network in an area due to bandwidth shortage while the other can still live with the current deployment? Many questions and I am looking forward to see how this will work in practice.