I'd begin by seeking the broker-owner of the of the brokerage that lists and sells the greatest number of luxury homes. The broker owner can cut the best deal as to commissions.
It would not surprise me if that broker had a partnership arrangement with a luxury home builder, maybe more than one.
Who is going to pay for the tear down?
Simply from a building code point, a rehab will be easier than new construction, but your list of contracts might be much shorter and total rehabs compared to new construction will take longer costing you more in labor and contractor's fees, I'd bet on that. Consider it both ways with the cost of the tear down.
The age of the house is a big factor as to hazardous materials, asbestos and lead remediation means much higher costs of a tear down.
If a contractor has no skin in the game, I'd bet too that the project will take even longer.
And, what is a 100% rehab, are you saying tear it all down leaving a wall to call it a rehab?
What do you have to contribute to a JV other than the property? Homeowner JV's are usually with contractors or investors short on cash or only getting in on the improvement side, they have to have some motivation as well. Why would a luxury home builder or upper end broker want to partner beyond the current value of the property?
Most likely, they will make (or get) an offer and move you out of the way, IMO. I would because the homeowner doesn't add value past subordinating the lot. They can do that at an agreed price and close prior to their sale sticking you with holding costs. Title isn't really that great of a factor for a licensed contractor, they have the option of using liens that can take priority over mortgage liens, the risk is built into their pricing to enforce the contract and secure their money. The value the owner provides is the buyer's/contractor's cost of money.
You could seller finance to a contractor and subordinate your loan to a construction lender, hope you have faith in the contractor taking a back seat to a larger first mortgage, or you have assets to cover yourself.
Also, as to lots in a higher end subdivision or area, the neighbors are prime prospects, some people are funny about what gets built next door or who moves in, so if they have the money and don't want to move, they might just buy it.
I'm considering doing that with one of my properties, just buy the place next door, it's why I haven't rehabbed it yet.
Don't forget word of mouth works pretty well in luxury sales.
Post some pics, get better valuations, holding time in that price range (?). If you're dried in, I don't see weather being a big issue. :)