Not sure why this is 'news' worthy, as many people (myself included) use epoxy to smooth and bind all the time.

I use everything from 5 minute to 60 minute epoxy. The slower the cure time, the stronger the bond, usually. I then will often cut whatever epoxy I'm using with Denatured Alcohol. I usually use 4 parts epoxy, 4 parts hardener, and 1 part alcohol to make the mixture much runnier. It does increase the cure time significantly, but this allows it to run a bit and penetrate where I need it too. The amount of alcohol can be varied based on the desired viscosity.

For example, if I want to reinforce a part that I designed to weak for the application, I'll coat the part with 5 minute. If I have a deep void (Like the keel of a boat that I'm casting with Lead shot), I'll use 60 minute cut with alcohol to let it ooze down into voids and openings. If you're looking for a decently strong, but ultralight weight filler, West System has a powder filler that really adds bulk to the epoxy without adding mass, but it does look like peanut butter, so it's not good for surface finishing, but is easily sanded and holds paint well.

Epoxy is a good smoother for nice even surfaces, but you can lose a bit of recessed detail with epoxy filling in the holes. If I know a part will be stressed alot, I'll Acetone smooth it to bond the layers better, and then do a coat of epoxy to harden the outside shell.

Remember, at low infills, unlike 'normal' materials, there is very little load bearing structure to 3d printed parts, kind of like how the world trade center was designed, the stress is transferred to the outside of the building / part. So unless a part will only receive compression loading, and even then, bonding the layers, and adding epoxy will greatly increase the strength.

If I'm going to be bonding two parts together, I try, if possible, to design the bonded sides to be the first layer of the print. That is usually your most well bonded horizontal layer, and takes sanding the best. I'll use a dremel with a medium sanding drum to roughen up the flat sides, and then epoxy.

If you want to get into epoxy use, I recommend the separate bottles instead of the dual syringe type. You will occasionally get uneven flow resulting in unbalanced mixtures. Excess epoxy or hardener will continue to stay soft, and even flow like tree sap if the mix off enough (My dad's boat has a tiny hole in the keel that has been oozing epoxy for 16 months now, looks like pine tree sap, and feels like it too). I've had structural failures from improperly mixed epoxy, as it never fully hardened. Get a jewelers scale (this is the one I use, it's great and cheap) that will do upto 100g, at .01g accuracy. Then pour in the desired amounts, using the scale to get within +/- 5% of each mixture. That will allow for a solid cure. For most applications, I'll use 1-2g of each, and .25-.5g of alcohol if needed.