I have seen people walk the whole of the IM marathon - as said, provided you're within bike cut off and can get a shufty on then walking the distance is feasible and within the rules. you cannot however crawl the whole distance....
I've looked through the regulations and the only rules to do with electronics etc. is to do with the bikes, or anything that can enhance you during the race that gives you an advantage over the field.
let's give you a little lesson on the rules of triathlon - and as an ITU official I think I have a good insight on this...
yes - quite right that the rules only state that you can't wear "socks" in the swim, but like all things technology is often ahead of the rules which are only reviewed once a year. generally, we like to work on the basis of fair play for all and we have a nice phrase in the rules which states in a number of places, "but not limited to" and another "penalise competitors who gain an unfair advantage" and finally "Officials base their judgments on whether an advantage, not intended by the Rules, has been gained"
that last bolded phrase is important that any triathlete should take note of, in that any triathlete trying to gain an advantage over another by use of any means and not in the rules can be penalised.
so, the use of shoes in the swim could be viewed as gaining an unfair advantage as it allows you to run from the water to transition with ease, whereas others have to run bare feet (or if allowed, put shoes on as soon as they come out of the water). equally, shoes could be viewed as a propulsion aid as they enclose the feet so act like a paddle (and a reason why socks are banned).
likewise, electronics and technology generally can offer an unfair advantage depending on their application.
there's a lot of interesting technology out there that can assist a triathlete in their performance but we do like to strip things back to basics and create a fair playing field for all irrespective of money or ability.
however, swim/run is currently not covered by triathlon rules (but who knows - it may be in the future) so designing a better shoe for that may be a way forward for you, or just a triathlon bike/run shoe
first off - you would not be able to swim in it as that's against the rules (basically nothing can cover the feet unless you have a medical certificate to show that it's needed ) so that element is a no brainer
so - moving on - you already have shoes that you can cycle and run in - they're called running shoes. most triathletes don't do this however as stiff soled bike/tri shoes are preferred for power transfer, but there's nothing to stop anyone riding in their running shoes, and then running in them off the bike. I'm not sure you can develop a running shoe with a stiff sole as they would be pretty useless!