This is an example of a classic Open Collector bus architecture using MOSFETS to achieve the open drain equivalent.
This technique was very common before the days of 3 state logic (TriState is a registered trademark incidentally) in discrete computing, where each processor register was in fact an octal D type latch.
The setup you have should work fine for what you want to achieve. Note that this is inherently safe, as the worst that can occur if more than one output is active at the same time is incorrect data.
The drawback is one of speed; driving a low onto the output will take a short amount of time, but the bus will have to charge back up before you could output a high (which would not change the state of the common bus line).
To say this is tried and tested is an understatement.
Edit: responded to number of collectors / drains
The number of devices on the bus does indeed affect the timing as they act as a capacitive load. The time taken to change the state of the line is proportional to R*C. The C term is constant and determined by the number of devices and the length of the actual common line. The R term is different depending on whether the line is being pulled low, or being released to go high.
When a single device pulls the line low (and this is affected by the number of devices as the single device turning on must discharge the bus from the high state which is proportional to the number of devices present) it is acting as a current sink with the drain to source resistance as the R term.
When it switches off, the R term becomes the pull-up resistor which is very much larger. This is why active pull-ups in 3 state logic was such a breakthrough.
The circuit simulator isn't working for me today (grr).
PNP. Emitter to +V, base to RTC through a resistor (100k\$\Omega\$?). Collector to boost converter, with resistor to ground (same as base resistor). Size the resistor for a happy medium between turning on & off reliably, and not consuming too much current. It should consume very little current when off.
Best Answer
The bottom of page 7-799 of the linked datasheet gives the thresholds for low and high input voltages given a couple of different supply voltages. As long as the voltage on the input is at most/least that value when referenced to ground the input is considered low/high regardless of what you tie it to.