sp3ctre said:First off, changing the forum would cause a massive drop in traffic, there's no two ways about it. Google simply hates mass change of content and url's. It may recover, it may not, but organic traffic to forums across the internet is at an all time low, so it's simply not worth the risk
You'll definitely notice a drop off to begin with but Google is pretty smart and you'll get re-indexed soon enough. Google (and other SEs) actually love Discourse because Discourse shows a very basic SE friendly site to bots (you can see this yourself by turning off JS on a Discourse forum). Out of all the forum platforms I have worked with, Discourse has been the best for SEO.
sp3ctre said:(and Discorse is awful, btw!).
I'm not sure which Discourse forums you have seen but Discourse was created by the same people who made Stack Overflow, and they have over 100 (paid) staff/developers and have received millions in funding... as a developer who has worked with all the major forum platforms I can confidently say that they really are currently the best forum platform around in terms of features, user-approval(once-they-get-used-to-it), etc.
There is probably one major drawback though, Discourse is aimed more at larger corps/sites and so other than basic customisation, you'll probably need a dev for customising it beyond a superficial level. Another downside is if you run ads (I'm not sure if you do, as my browser usually blocks them) then you will be limited by their ad plugin and placement, so this could be frustrating.
If these are a consideration for you then you may want to look at Xenforo instead (currently the 'best' of the forums that is closest to this one, and easy enough for non-developers to customise).
Whatever you decide, good luck - I much prefer supporting independent platforms like this than big US-tech companies like facebook, twitter, instagram, reddit etc, hence thought it was worth making this suggestion.