I haven't found an answer to this specific question on BP or elsewhere online: if I die, and my SDIRA that holds investment property goes to my adult child, what are his/her options? 

If at that time a child wants to move into the property as their primary residence they will be able to keep the reduced property tax basis.  

@Kirstyn Indy - I would start off by calling the credit card(s) that you wish to add your child as an authorized user. 

Instead, open a Roth IRA for each child and deposit their income directly into the IRAs.

That's a disaster waiting to happen.Unicorns are cute and all, but being a unicorn hunter is not a good career path.Now go, my child, and sin against the market no more. 

Probably child’s play for a cyclist like yourself.

We are already a fortunately high net worth family. however, that is from my spouses W2 income, so at this stage we don’t really have anything tangible to “leave behind” and we want to try to build generational wealth for our child. 

Child sustained broken leg and concussion from falling through rail spindles that were too far apart. 3 days in the hospital, surgery

Your wife as joint tenant (even though she isn't an active manager she can still sign a check if need be), a child or trusted relative as a designated beneficiary (so the bank knows what to do with the money).

GROSS Income x 45% >= Rent + Monthly Debt PaymentsSometimes people have enough income for rent, BUT they have outsized monthly debts (child support, large car payments, credit cards, etc).