1 Each individual chooses his or her default visible trust algorithm, and can change its parameters freely independent of client.

2 Yes, No. And, 'Is trusted' is not granular enough. 'Is trusted in meatspace' vs 'is trusted globally' vs 'is not untrusted' vs 'is prolly not a fed'

3 Absolutely not. A user should have the freedom to follow someone they do not trust without it affecting their WOT algorithms, if they don't want it to.

4 Require? Perhaps not. An option though. 'Create Throwaway Filter' or 'Create Persistent Filter' or 'Edit default filter' or 'Change default filter' -- these should all be independent of client

5 I'm not sure the implications, but it seems not only by clients.

I definitely think there should be a market for filters. I need to be able to click and see 'what do employees of x company' tag this image, say about this fact-check, rate this person's trust, etc.