I realise that your initial point was that it would be great if you could get elite status covering both VA and QF at the same time (and I agree with that), but can you clarify how you think a "semi regular flyer" is going to earn elite status with QR? How do you define semi-regular - one domestic trip a month? I don't think that would even get you to Gold with QR, even if combined with an annual trip to EU (in Y).
In fact, by my calculations, 1 EU trip per year + MEL-SYD rtn in every working week of the year wouldn't quite get you to QR Platinum.
Getting Velocity status is actually pretty easy though, especially if you can exploit family pooling. You could almost certainly get to Velocity Platinum with less flying than you would need to get QR Gold.
SYD-DOH-LHR return in classic Y - 86
SYD-MEL return in classic Y (flying QF) - 10
For 48 weeks = 566
Enough to retain, but not attain QR Platinum.
If on QF:
SYD-DXB-LHR return in Y - 190 (QF marketed EK flights for the closest comparison - but same via SIN or direct)
SYD-MEL return in Y - 20
For 48 weeks = 1150 (+50 loyalty bonus)
Enough to retain, but not attain QF Platinum.
But pretty easy on both counts to build up the status by connections instead of flying direct.
It's a bit of a moot point though - as QR doesn't give qpoints for non-oneworld flights as far as I can see (not even LATAM who only recently exited) so unlikely they'll give to VA unless booked as QR flights on an international connection.
Definitely easier to maintain WP on VA - only 40 return SYD-MEL trips, no European trip required.
But then again on QF - if you were to be in the US, you could do a oneway trip in F (2 legs) for around US$500 and earn about 140 SCs - equivalent to 7 return MEL/SYD trips. The same trip credited to QR only gets you 25 qpoints.
Personally, there's no way I could retain QF WP without domestic AA trips in F.