Well, how conservative do you want to be? Notation changes over time.
You might even ask why you need to keep repeating the '3', as you would not for fully notated triplets.
Your slash shorthand seems both clear and logical to me. If you start with the fully notated triplet for one beat, then follow it with the slash shorthand, it should add further clarity.
One thing to consider is whether the most economical thing is to notate the full 3 note triple and omit the repeated '3', that's the common thing, or use your slash shorthand. It's possible that the repeated '3', potentially all over the place on the page, would become distracting. Given notation standards, numeric figures in a score tend to draw attention to some significance.
Even outside of music notation, text is a significant attention grabber. When I watch movies with my wife, whose mother tongue is not English, we put English subtitles on for her benefit, and I have a lot of trouble resisting reading them... even though I don't need to. That last part if my main point. It could become a distraction simply because it is text.
While I'm sure no one here would advocate this, and I wouldn't use it, I wonder: if this is normal...

...then why is reducing it further to...

...a problem.
Of course that is a rhetorical question. But it's the logical conclusion of shorthand reductions. And as circumventing the repeated text '3' issue, maybe it's a better proposal? If you were actually trying to change conventions.