interesting thread. i had just (last night) googled MMM for traditional vs roth 401k. first couple of hits were from 2012-2016 timeframe and the overwhelming consensus was that traditional was the way to go.
is the new tax code dramatically different to impact this thought process? or, is it mostly an impact of folks living the MMM FIRE lifestyle? i mean, 22% is the old 25% and 12% is the old 15%. it seems like most here are generally in the 25%+ bracking during their working days. so, the relative delta seems like a wash.
Remember that most of the individual tax provisions of the TCJA sunset in 2025; also, an intervening Presidential election could give the new administration & Congress opportunities to change the law before then.
While it's difficult to make accurate predictions, especially about the future, it seems likely that the TCJA will expand the deficit and provide most of its benefits to high-income and high-asset taxpayers. The expansion of the national debt as a percentage of GDP, in advance of the coming gap between Social Security and Medicare benefit payments and taxes, along with the perception that TCJA skews most of its benefits to those most able to pay, together will argue for an increase in marginal tax rates. Furthermore, public support for the TCJA is perhaps the lowest ever for major legislation, and my unprofessional reading of the current press argues for a political backlash against the GOP, at least in 2018; OTOH, voter memory seems not to last longer than a whore's moan.
Therefore, I bet that you're better off paying the current 12% or 22% rates by using Roth retirement plan options than you might be some years hence.
Employees (such as I) who will receive taxable pension income would also benefit by contributing to Roth now, as the pension income will fill up the lower tax brackets in retirement.