I teach in an urban environment and worked in a rural environment prior to now. Thanks for assuming I don't know how this works.
In small towns, most people live far away from each other - but they're willing to come together to rideshare or carpool. It can be done easily if you get on it ahead of time and communicate consistently and effectively. I've had it work myself many times.
In urban environments, there is also the factor of mass transit to consider. Most kids are a short bus ride from home to school, if not a train ride or the like. There are many, many more options for urban students than suburban ones. Your argument doesn't hold water.
Now, as to your other points.
Find a single football coach willing to play with "just 30 kids" when they have 50 that want to be a part of the team. Here's a hint: You won't. Coaches will put their foot down about allowing their kids to participate, and you can follow along. Your coach will be your best advocate for getting people to your practices in these cases!
And - again - your die hards will show up no matter what. Your middling kids will show up if you make them WANT to be there. Knowing they can see their friends, that they're going to march, that they're going to get the full experience - that will get kids to come to practice and games. If you honestly think you're going to lose 40% or more of your kids if you don't see them every day, you're doing a bad job as a director getting those kids invested in your program to begin with.
Again. Find solutions, not just problems. My current admin has a rule - you're not allowed to complain about a problem unless you've come up with at least one solution to the problem. Isn't this what we want? Figure out how to make it work, then DO IT. Stop saying "it can't" or "it won't" - if this comes down, are you just going to throw your hands up and give up on the season? I bet your admin won't support that. Find a way to MAKE IT WORK.
But finding solutions comes from finding the problems. And your answer is very suburban centered. The urban and rural families will have much more difficulty with that.
Football needs 30 kids at most. Sure, they have 90 on the sideline but they need 30. The small schools probably need 15. Don't think ALL those kids on the sideline are die-hards. So you will see the number on the sideline drop. Basketball needs 6 kids. Maybe that's okay. You will see the biggest drop in the JV (NV band), kids. But maybe those kids that don't get playing time are still learning something by being at practice but won't have that chance because of transportation or moderate interest so the parents don't push it. Look wholistically at what athletics teach and who benefits. Often times, like in band, it isn't the superstar the learns the most. It's the kids that work the hardest that learn the most. But we take away those opportunities when we set up a system that only the "die-hards" are allowed to participate.
Band literally needs everyone. So you have set yourself up for 60% attendance rate? And you are really going to sideline every kid that doesn't come to every rehearsal? Maybe you can do that in your program. I don't know any that could function like that.
And if the who purpose of the schedule is to limit the number of bodies and the frequency of kids on campus then this becomes more work than it's worth because you now have, depending on the size of the school, hundreds of kids on campus every day instead of every other day. And this isn't just sports and band. What about the SPED kids that need daily services or extra help to keep up educationally. Maybe it's time to listen to what Dr. Paul mentioned today and go from there.
How is it going to HAVE TO work for sports in that situation? If a kid is interested in performing/playing, they need to find a way to get to practice. That's how it is. Especially with sports like football, where they are literally required to have a certain number of practices before they can even be issued a helmet!
Set up carpools. Set up rideshares. Maybe you can get groups of three kids involved so that parents only pick up or drop off twice a week and after games. It can be done.
Yes, it's inconvenient. Yes, in some cases it may not be possible but to simply say "it can't be done" because it's inconvenient is not going to benefit anyone.
Find solutions, not more problems.
How would daily after school activities work? How are the kids supposed to get there on their off days? Are we just assuming parent taxi service is sitting at home with nothing to do but shuttle their children around?
I would recommend that you be proactive to get your band rosters established and create the A/B lists and push to have assigned days made by singleton class rosters, rather than alphabetical or grade level.
Also push for after school activities to go on a daily basis, if possible.
How is this any different than a school that operates on block schedule?
Plenty of bands out there only see their kids every other day. Schedule the top band on Mon/Weds, schedule the second band on Tues/Thurs, and hold after or before school practices for full band marching (or the Super Tuesday thing that I know some folks do, where they go 5-8 PM once a week).
You won't be competitive at the state level but you can still be a quality program.
The school where I retired from (band director) five years ago and where my daughter now works may go to a schedule next year where 1/2 of the students only attend on Monday and Wednesday while while the other half attend Tuesday and Thursday. I can't imagine band as we knew it functioning in that situation. You better stay abreast of what your school is planning, or should I accept the fact that things will never be the same?