Since I recently got some serious teeth issues, I profoundly support this idea!
I did some research and found the products the same as you described them. For example, this temporary tooth filling material repair kit ( or this, too) costs only 8 GBP and can help your lost fillings or secure loose crowns., caps, etc. It's safe to eat, easy to use and there is material for 24+ repairs in the set. Really cheap! Here is a video of a guy demostrating how it works.
However, none of the above-mentioned products are advised by dentists. If the bacteria gets stuck under the filling, it can make the cavity even worse and end up destroying your tooth. If you watched the video, the guy said "the product worked perfectly and it saved him a lot of money" (he didn't go to the dentist, because "he didn't need to"!). Another problem is that if you leave the filling to high, your bite may change, putting more pressure on the broken tooth, causing more damage to the nerve.
Although the product exists, I would like this topic to continue in any way. Therefore, I propose some of my ideas for you to think and maybe get some cooler and more innovative ideas.
when the DIY dentistry kit gets opened, the counter starts whichconstantly reminds you to go to the dentist
when the kit gets opened, the dentist receives the notification and send you the date and time of the appointment
red fillings remind you everyday to go to the dentist
you are able to buy the kit only if you schedule a dentist appointment, too
Please leave the feedback on this idea