Again, there is still no conclusive evidence on just exactly how much serum, scalp, and intrafollicular DHT each contribute to the process of baldness. Topical 5-AR inhibitors like Alfatradiol work to a degree, which means that reducing scalp/intrafollicular DHT can and does help against baldness even without a reduction in serum levels. A more potent topical inhibitor such as S-Equol could potentially be strong enough to stop hair loss in most people with no systemic reduction.
Your 'Local DHT receptor blocker' is already here, it's an androgen receptor antagonist called RU58841. On average it works more poorly than Finasteride because blocking of the AR is NOT enough to prevent all the destructive effects of DHT, one of it's more significant damage pathways is through
interfering with the estrogen receptor. AR antagonists cannot help with that angle and will be inferior to a treatment that can bind or remove DHT in its entirety.