It makes me wonder why ICAO continues to use the semicircular rule, when simply deleting it would apparently make us safer.
Imagine an Airway running 230/050. Isn't it nice to have a system where when you leave that airway eastbound, you will be at an odd level and any traffic in the cruise westbound to join that airway will be at an even level even if they are not talking to ATC yet.
That is why I say it is a system of organising traffic which does work but it is not designed to make it safer. The only natural separation in the ICAO system is VFR-IFR during the cruise (500ft).
Finally you have to remember that as far as ICAO is concerned, in class F and G airspace, separation is not provided to all IFR flights and as such they will never attempt to try and say that anything one does in IMC in such airspace is by definition safe.
I suppose what you have to ask is the reduction in head to head conflicts between traffic on 090/270 increasing the safety level to a greather degree than the introduction of crossing conflicts 179/090.
ICAO will probably point out that in the crossing conflict the aircraft on the right was right of way and the other shall avoid it. Which is 100% correct but very hard to do in IMC whereupon ICAO says, if you are worried about that then start will controlled airspac class E.
There are so many interlaced rules that rely on each other without one realising theri significance.
eg Airspace Base should be a VFR level. Therefore, if there is IFR flight cruising in class G below the base they will be no closer than 500ft below so traffic in the system 500ft above is 1000ft above the other IFR traffic below. VFR flights can cruise at the base (in VMC) so that IFR flight 500ft above gets the standard ICAO 500ft from VFRs. Thus the systems are complimentary.
For an example outside controlled airspace let's look at the ICAO system. IFR flights above 3000ft must cruise at whole levels, VFR flights at those levels +500ft.
In the same airspace VMC minima require VFR flights to be a minimum of 1500ft above or below cloud.
You may not have realised it previously but when one combines those two rules, you will find that an IFR flight in cloud will be a minimum of 1500ft above or below any VFR traffic so they can climb or descend 1000ft as they change direction in IMC without having to think about VFR traffic.
So if you want to delete one rule there could be many consequences you did not expect.