There are four VGA mostly incompatible systems in Europe plus one each in Korea and Japan.
Existing VGA systems have been around for up to 40 years (Talgo) and perhaps 10 years with SUW, with 5 years of continuous daily practical testing for the latter. VGA offers the prospect of merging the Russian BG zone with the European and Chinese SG zones.
Speaking for the SUW 2000 system, so far the system has between used between SG and a wider gauge, but not for SG and a narrower gauge, where there is less room between the wheels for the VGA stuff and the disc brakes.
Similarly there is not specific mention of the possibility of handling more than two gauges at once, such as BG, SG and NG in Australia. Since the VGA may have holes for the wards of the locking mechanism, particular combinations of gauges may be ruled out.
So far, VGA for locomotives (which also need space between the wheels) is at the toe in the water stage.
So while considerable progress has been made, there is a lot of uncertainty as to what the situation is.
Some of these issues and possibilities have been discussed in the "Benalla-Oaklands Railway" thread.
Comparing VGA instead of Gauge Conversion:
* VGA has cost the advantage if (just wheat) traffic is low and the line is long.
* GC has the cost advantage if traffic of several kinds is higher and the line is short.
* VGA has a disadvantage if custommade VGA bogies are needed with a long delivery time.
* VGA and is gauge orphan branch would probably need to piggy in/out track maintenance machine, which may not be easily fitted with VGA.
* GC on the Oaklands line benefits from long track possessions.
* Dual Gauge or a separate SG line from Dynon to Frankston and Eastern Victoria would on the other hand very difficult.
In the above map, showing the current situation with SUW 2000 VGA, Pakistan is shown SG (red) when it should be BG (blue).
The map also has an inset with a picture of the SUW 2000 Gauge Conversion Track, which is quite small compared to a bogie exchange or transshipment yard.