Since I've upvoted whatever I could, it is now time to comment - I put it off so as to give myself time to think.
In the steemit editor, I use html - only because I know how to use it. However, as do many coders, I suffer from Carpal Tunnel Syndrome, so having to place the markers for opening and closing paragraphs for each paragraph, means my hands are in pain by the end of my day. So I am looking forward to seeing how yours works.
As for the matter of beneficiaries: I assume it means I am designating that the income from my post (upvotes received) will be split, the 10% as noted, plus 90% as I choose...but that comes from the 50% I am receiving in Steem, not the SP part? If so, it means you are actually getting 5% of the total? Is that after the curators have taken their 25%? I ask as I saw witnesses discussing changes to the curator earnings (they say that posters are not important to steemit, only the curators, so they should earn more, and the poster less - if I recall correctly, somewhere between 35 to 40% for curators).
I am not going to volunteer to test since, as you know, I am using an older system which finds ways of causing problems :))
Now, something so simple I am embrrassed to ask, but I've never seen anyone explain it. When I use steemit, for certain processes I am asked to login again and enter my password - either the posting one, or for transferring funds, the active one. It is that simplistic for me. Then I come across you asking for a keychain. Is that a different wallet with other passwords? For instance, I created a Steem Keychain (through steemengine) but I cannot use it as it needs me to move to at least Win7. When I can buy a small harddrive, I intend moving to Mint (Linux) so not going to Win 7.