I'll weigh in with a few thoughts. First, thanks for even asking, Carrie. I know how seriously you take this and it means SO much to me and my family! I have loved talking high school with you at the conventions and seeing your passionate heart about this subject. I have complete confidence in trusting our high school years to HOD!
This is our 5th year with HOD. We began with Bigger Hearts and are currently using Rev2Rev with two 7th graders and a 9th grader. I LOVE the format that you already use, Carrie. It is one of the big draws to HOD for so many people. There is NOTHING else out there like it. Doesn't the saying go: If it ain't broke, don't fix it!

For me, it is the content that is more important for high school level, not going to a weekly grid or something similar. I think someone else mentioned (was it you, Carrie?) that kids in public HS aren't given weekly assignments and then told to figure out the schedule themselves. I think we are always in a rush as homeschooler to start college before HS ends. This is the only time they have and I'm not in a huge rush to make my high schoolers into college students. I think the daily format in HOD is still excellent preparation for dividing time into daily chunks to make real progress.
I do have a few thoughts, though, based on using HOD with a high schooler for the first time this year. We have had to beef up Rev2Rev to count for HS credit. To do that, I have assigned various books, videos, narrations, etc., to my high schooler on a weekly basis and allowed her to decide how to complete those assignments each week. This has taught her time management and how to divide workload appropriately. But the bulk of her work is still in the daily HOD format which works wonderfully! So, to me, it is the best of both worlds this way.
So...would it be possible to do high school HOD years in a similar manner? To do the bulk of the schooling with the daily format as always. Then, choose a subject or two - (ex. Govt. readings, Lit 3x/week, Grammar 3x/wk) - and give the weekly assignment on Day 1 - and allow the student to divide the work as they choose for the week? This might not be feasible or make any sense, but just thinking through this.
Also, to save space on the boxes since you will need more space for the high school subjects - would it be possible to not even include the Math, LA and any other repetitive subject as a large box on the page, but just as a small reminder line or small box each day? Certainly, I don't need the key idea in those subject areas daily, which would save space.
Also, I really like your point, Carrie, about spending the time with the books themselves rather than reading through voluminous teacher notes such as are included in SL guides. I have 5 children, ages 15 down to age 4, and some with challenging issues - so it's not like I have much free time. I just make it a priority in my time to read through the history, science, Signers, and inventor reading each week for the week coming up. This really doesn't take long at all (maybe an hour to an hour and a half weekly) since the daily readings are not long and I'm not doing the assignments with the readings. And I figure when the youngers come up through that guide, I won't need to read the books beforehand a second time!

This is an invaluable investment of my time to be able to have a working knowledge to discuss with the kids and keep up on what they are learning. Plus, I consider this "me" time, too, since I love to read and I love to learn and I rarely have time to do any other reading!

So, for me, lots of teaching notes would not be necessary and I know you certainly do not have time to do that. The other resources I can skim quickly enough while discussing with the kids.
I truly can't WAIT to see what you come up with next, Carrie! I'm praying for you as you make these decisions.