Something around the "attention" is a very good way to pump that flywheel for premium. Sometimes people just want to pay to be noticed... to be heard... and on the blockchain, this is difficult to be noticed, hence why an UI can really make a value proposition in terms of adding that feature for value.
I would defiantly say that with something along those lines (and there could be several levels like X has...) I would be perfectly happy to pay, to be heard.
Example:
Normal Premium = just new features...
Premium+ = Same as Premium, plus all threads to immediately join threadcasting in the top, for 24 hours.
Premium++ = Same as Premium+ but instead your threads stay for 3 days.
And so on...
(this is just an example, but you get the idea)