So I did not get any useful suggestion other than "test it first". So after some test on new and old paint, I pulled the trigger on using it as porch "paint" and have been pleased with the final product...so far.
Of course not all sealer are the same as paint, but the latex/asphalt based, as it seems to me, is pretty close to paint. What I used is Latex-ite rubberized asphalt and sand mix from Home Depot.
To prepare the surface, I scraped loose paint, repaired rotted-wood, lightly sanded the entire porch, and applied a single coat of Zinsser 1-2-3 primer. And this is what I learned after applying the sealant, mostly with an ordinary roller brush:
After about a weeks worth of foot traffic, it seems to hold up pretty well. Of course the real test will be 1 or 2 yrs worth.
Applying it is different than with paint. Whereas paint is tacky on contact, the asphalt suspension is not. On smooth surfaces, the suspension just does NOT stick upon application. You can't use the squeegee method and roller brush works okay, but you really need a light touch: the heaviness of the suspension impedes the free rolling of the roller brush, and you end up pushing the suspension around. Even with a light-touch, the roller left a lot of bare patches that needed a second coat to conceal. However, I can confirm that roller brush works well for that second coat, after first coat cures and the surface takes on some roughness. Indeed, squeegee might also work as well, but I don't did not try it.
The upside to #2, however, is that clean-up is much easier
than with paint. Whereas it was hard to clean primer that I spilled and let stand for as little as 5 mins, the asphalt was super easy to clean with rag and water, even after 30 mins.
The texture created during application really stays in place. I
could see all the brush and roller strokers clearly after 24 hr cure
time--much more noticeable than with ordinary house paint.
Fortunately, I took the time to keep the strokes even and straight,
so the final product does not look messy. More importantly, given
that texture was an desired feature for me, the end result--a very high-traction surface--is perfect.
Finally, the finish, like a driveway, is quite matte and black.
In low-light condition, it's like looking into a bottom-less abyss.
Ordinarily, this would be cool, but I do find dusty footprints to be
more noticeable in the bright light of day. I don't know if its
the blackness that makes the dirt stand out or the roughness causing
more dirt to be left behind or both, but aesthetically, the use of
this product as porch paint could be an issue, especially with a
covered porch, with limited rain exposure.
With the exception of #5, so far I find the asphalt-latex sealer to be a resounding success. I like the final finish and seeming durability. Of course, there are porch paints designed specifically to achieve the same results, but I'm pleased with the use of driveway sealer as porch paint.
I look forward to seeing how it performs under and holds up to a cold winter: with salt and shovel use as well as heavier boot traffic. Hopefully I will remember to update this post next summer.
UPDATE 11/3: After a heavy flow of Halloween trick-or-treaters, the sealer held up well, albeit with lots of dirt due to surface roughness.
UPDATE 08/2018: After a whole year, I can say the Latex-ite worked reasonably well. It provided significant improvement in traction with snow and withstood foot traffic fairly well. Where foot traffic is light or non-existence, the rubberized coating did extremely well. Underfoot, however, it was mixed; that is it mostly stood up to wear and tear EXCEPT at the floorboard joints. At the board seam, the coating crack and did exhibit additional wear from foot traffic. Presumably thermal expansion and the flex in the board was too much for the rubberized coating to withstand. It is not obvious, on the other hand, that regular deck paint would have done better. One regret I have is that while the coating did significantly improve traction with snow (which was the main objective), it made clearing the snow off the deck harder--residual thin coating of snow always remained after shoveling, cosmetic issue only. I would presume that this is an unavoidable compromise with any textured deck coating. In conclusion, after a year, I would say that functionally the latex/asphalt/sand mix worked fairly well as deck coating.