Immediately, I performed a Roth conversion, and instead of paying taxes on $50K I'm paying taxes only on $21K.

Where is the income tax of 49% here?

Is an IRA subject to capital gains tax?

So the question becomes based on their individual and personal tax situation what is the estimated tax burden they'd save? 

Being a real estate professional allows you to treat the income as non-passive, allowing higher high income tax payers to pay less in taxes.

Tax-Free Exchanges: While 1031 exchanges aren't available to SDIRAs, the tax deferral within the account means you can sell property and reinvest proceeds into new opportunities without immediate tax consequences.

This appears to be a 'transfer tax' instead of an income tax. 

Consult your local CPA to calculate accurately and minimize your tax liability.

If you think ahead, you can minimize recapture with the right tax planning.So what is recapture?

It is my understanding that the new owner will have the house at the cost basis of my purchase price, for calculating capital gains taxes or depreciation.For gift tax purposes for you - FMV.For capital gain tax purposes for the recipient - your original basis/purchase price