If you decide to retire early you can always set up a Roth conversion ladder by rolling over IRAs and 401ks to Roth IRAs. It takes 5 years for those contributions to "season" so that you can take them out before 59.5, but you can take out capital gains that way as well. No need to contribute to a Roth today if that doesn't make sense otherwise.
Can you elaborate on this? I've been managing a post-tax account somewhat like a Roth IRA, though it is not an IRA because I plan to retire far before 59 1/2. I'm hoping for something in the middle of the two approaches with flexibility to withdraw early without penalty.