That is the tool I want to be available most rapidly, so a steerer mounted one would be ideal. To me that would be more useful than a mutlitool.
Daft question but what’s your logic on this?
You’ll very rarely use it vs a multi tool.
The ease of access for a multitool is actually very useful, changing it from a “next time I stop” to a “right now” job, a tyre failing to seal badly enough to need a fix is never anything other than a now job.
Being able to leap, catlike, from your bike jabber doofer in hand isn’t going to save you needing to reinflate the tyre, so you’ll need the pump or co2 out anyway which will be buried somewhere else.
Repairing the tyre isn’t going to be especially quick because of the above regardless of your ability to react to it quickly.
I’ve got a few of the dynaplug ones, they look very good, the co2 especially, but I’ve only actually used any of them once in about 5 years.