I'm missing something here. You can already easily maintain constant direct level with a series delay or reverb, while still having control (even external control) over the delay level (via delay input gain), mix, and overall level.
Set the mix to 50/50 and use the delay input gain to adjust the level of the delay. If you want the direct to be unity gain when the delay block is active, set the level to +6 dB. What is the advantage of this proposed "fix" that would outweigh screwing up the levels of existing presets?