LiquidThreads was an unmitigated disaster, in my view, and has made the site worse for being here. History before it was enabled was lost (or, at least, very hard to find) the links in e-mails never take you to the thread they're supposed to, the UI is horrible and it is difficult to find things you are looking for. It actually makes the site harder to use for anyone at all experienced in wikis, not easier, and so should never have been enabled.
I haven't used Flow, so I don't know how it compares, but I would certainly vote for removing LiquidThreads! If Flow actually works in a wiki-like way (i.e. you can view history, see the state of the page before it was enabled, edit comments where necessary, etc.) then I might be persuaded that it is a good replacement, but given our experience with LiquidThreads I am fairly sceptical. For it to work it would have to be something that works inside existing wiki pages, rather than fighting against them. It would also be a requirement that all LT content can be 'migrated' to Flow so that it is not lost or broken. It is not acceptable for it to simply be shunted off to an 'old threads' namespace and abandoned - it needs to appear where it was originally posted.
The issue is as much about how the extension works behind-the-scenes and how well it integrates with the rest of the wiki, as about the interface it provides.
For example, I don't want to lose my current talk page, nor its history. If what is there can be converted seamlessly to Flow, without losing my ability to view old revisions of the page (pre-flow and post-flow), archive things in the way I have done in the past, include some non-thread-like content (e.g. introduction section) and link to specific items without the links breaking as items change (e.g. if they move to 'page 2' of the listings) then it might be viable. Otherwise, please just remove LiquidThreads and don't mess up the wiki with further incompatible plugins.