We did wood laminate floors and were advised to do hardwoods on the stairs because the wood laminates don't last as well on the smaller surface of a step. The wood laminate is a floating floor system and the small size of a step doesn't have much room to float/give....I don't work in the industry; this is just was what I was told when I put my kitchen floor in last summer. The guy who put in the wood laminate didn't really want to deal with building out the hardwood steps and the cost elsewhere made me reconsider....we are now doing carpet on those steps because the other room is carpet and really, really needs replaced.

We did sample NATURALE and TRAFFIC without the sealer... They look perfect and do hardly give any darkening effect... Bona Kemi technical advises against this , because of the risk of sidebonding.. We just tried it on a small area and only a few days ago.. Is there anybody out there who applied NATURALE OR TRAFFIC without the sealer a longer while ago and on a larger area?? In Europe you can buy NATURALE as a ONE component finish, to be used WITHOUT a sealer...( In the USA only the 2 component is available and is recommended to be only used WITH sealer)

have also been reading about a diy finish made of equal parts boiled linseed oil plus turpentine...but now I'm getting out of my league...anyone been there done that?

Shellac is a natural finish. It is a miserable choice for your purpose, however. Varnish and polyurethane are not considered toxic when dry by most of the testing labs. Regular 2x4's were also a bad choice, unfortunately, as they have almost zero moisture resistance. And trying to protect them with a finish is just about as useless in the long term---meaning in a year or two you will see a total breakdown of finish and wood. Using a decay/rot resistant wood is a better alternative. Or even composite decking---that might be my choice as it will not be affected by water.