Two more thoughts. One is that it would be undesirable to run 3-phase motor loads (even very small ones) at the end of the submain when two phases are loaded up to what I assume is a VD-imposed limit while the other phase is light. The voltage assymmetry will cause increased stator current and heating.
If there are no 3-phase loads to power, then depending on the machine, if it is tolerant of low input voltage it might be possible to convert the SWA submain to two 2-wire single-phase circuits. One loaded to the 16A limit to serve lighting and general loads with its original VD spec, and the other uprated to 25A with higher VD permitted for the single machine load.
Good point about the voltage unbalance, applicable in all cases of course, but you're right this would be a particularly severe case with two lines right up to their limit, and the other potentially fairly unloaded.
I would rather double up the four conductors for a higher current rating, two for the Neutral and two for the line, but it all depends if the rating limit is due to cable, or fuse/supply limitations.
The former would be easier, no good if you have 3ph loads, or fuse/supply limits.
In that case it is either a no-go, or you need to use all three phases equally, so a three phase to single phase transformer would be a must, you could either use a Scott connection, or ideally a Le Blanc, both giving proper 2 phase - where you need to use both lines, ignoring the 2 phase neutral, so voltage wise you need a 163V ph-n supply give 230V ph-ph (1.41 factor).
The most simple solution of three 400/115V transformers primaries in delta, two secondaries in open vee, and the third reversed on one end of the open vee; wouldn't really be suitable as it presents quite an unbalanced load between phases. Not quite as bad as just a single line-line transformer, but you could get the full 32A.
