I know nothing about this, but there's a flag on https://m.reddit.com that says "Beta", and on https://i.reddit.com there's a link to "try the beta", so I think it remains to be seen whether the old version is still available when m gets out of beta.
That's more than I can say for many, many other things, where whether I like it or not I'm forced to have the latest design fad (flat, pastel colours, long and inefficient animations and huge, unnecessary padding nowadays) shoved down my throat.