I would think it worth exploring SDC variants, and identifying capsules that are more 'in the direction of' the specs found in the Sennheisers, both LDC and SDC.
So far, I have only experimented with a variety of cheap Chinese 34mm capsules -- both centre and edge terminated.
The chance to try out something more appropriate to the concept -- like the Sennheiser 'push pull' capsules -- would be a fascinating next step to try.
Sadly, the prices of actual Sennheiser capsules are WAY above my hobby budget, and I've not seen any others of that type offered.
I'm guessing Rode must have their own 'RF' capsules for their range - for example - but I've never seen any offered for sale? (Understandably).
It has been interesting to note how 'standard' cheap capsules seem to react differently when biased with a few volts of RF - rather then 60 or 70 V of DC.....
Although I don't have test equipment sophisticated enough to be able to measure those differences objectively.
There is quite a variation in the sensitivity of the different types of capsule - with the 'K67' types seemingly more sensitive than the K47 types. That presumably has something to do with membrane tension .
Sadly, discovering which cheap Chinese capsules are built with lower tension membranes seems to be largely a matter of luck... The published 'specs' usually appear to be just a bunch of numbers picked out by the marketing guys....
All enjoyable experiments though !
I'm tempted to try your circuit with a Neumann TLM67 I have, since I have a spare set of Neumann metalwork....
I'll look forward to reading about what you discover -- when you get the chance to try that...