whereas it would help trans men feel more validated perhaps.
It's none of my business what they choose to do and I wouldn't seek to dictate to them, but I can't help thinking that, if you have spent a large part of your life being identified (wrongly in your opinion) as a female when you clearly wish to be recognised as a male; and you have likely had a lot of struggles for acceptance as such - it would seem to me that the very notion of doing anything that could possibly risk your being in the position of what is seen as probably the most distinct biological marker of a female - that of being pregnant - would be utterly anathema to you.
As for 'centring women' when talking about pregnancy, what proportion of the adult population consists of transmen? Then, of that tiny percentage who are transmen - i.e. people who do NOT identify with taking a female role in society - how many of them will be in a position to ever become pregnant?
Of course, the answer is not zero as there will always be an extremely infinitesimal number - but even then, they will clearly understand and accept that they are in such a tiny minority of a tiny minority and make adjustments accordingly, with the normal discretion and dignity that anybody would.... unless, that is, they are deliberately doing what they are doing in order to seek attention and/or to climb on a self-publicity bandwagon.
Considering that, when examining people's methods of transport to an event, official surveys will usually offer options including car, bus, train, on foot, by bike (one from our Midlands LEA asking how our DS travelled to school even offered 'via London Underground' as an option). However, I have NEVER seen an option that would apply to a wheelchair user who is not using any additional means of transport. Considering that the number of wheelchair users is manifold more than the number of pregnant transmen, I wonder why the one minuscule group is so desperately important to describe so precisely whereas the other much, much larger group is effectively brushed off and told "Well, you know what we mean - just choose the nearest and don't try to be difficult about it." 