I haven't simulated your oscillator, but I imagine that lower values of R1 would increase LC damping? - dewster
yes
R1 may also vary the drive / antenna phase?
probably yes. The low pass R1, C_inTLC555 generates quite a phase shift at 1.5 MHz though I did not get deeper into this with sims & measurement
I imagine that the feedback would necessarily need to be DC for that to happen?
yes, that's why it took an extra feed back resistor in the capacitive divider version. I've added my LSPICE sim to my homepage docs, so you can play with it.
How is the drift over temperature / time?
I did not investigate this. I only can tell, that some builders were surprised about the stability over time, despite the high RF/ audio freq. ratio.
And there is hope if there would temperature stability problem: due to the voltage controlled detuning, it should be possible to add a resistor/NTC-combination voltage divider in front of the LM317 ref. input to get a temp. compensation for a certain tuning range.
For my applications I'm ok with the stability as it is, so I also do not need to go deeper here