The following looks like a good article on this kind of question:
Specifically look at the section,
Can I connect multiple devices to a single Thunderbolt port?
Thanks. Useful text. It seems to contain a positive answer, that connecting a non ThBt device at the end of the chain does not affect upstream performance and that the display must be the last device in the chain as it is not pass thru. It specifically mentions displayport as a working example. Not conclusive but close.
Until such adapters are available, one of the biggest Thunderbolt challenges will be that your display must be the last device in the chain, because the new MacBooks have only a single Thunderbolt port and current displays—even those with DisplayPort connections—don’t have a way to pass data on to another device. This will make it a hassle if you want to temporarily connect or disconnect, say, a Thunderbolt hard drive, as you’ll need to disconnect your display in the process.
If you connect those devices to the end of your Thunderbolt chain, they should’t adversely affect the performance of faster “upstream” devices.