I'm currently designing a ROM hack that is pretty much linear with secret exits that lead to other levels that lead to switch palaces. There is also a special world that can be accessed by finding all of the switch palaces. There are also some extra goodies in it.
Seems fine to me. I'll admit I find it a bit more interesting if there is a bit of nonlinearity to the overworld map (like how the original SMW did it), but I won't hold a linear overworld against a hack if the levels are still good.
You have audience, but I would rather play a hack with a lot of split paths and secrets. I have more fun making hacks like that as well, but it depends a lot on your concept - Challenger (an old, forever on hiatus C3 project of mine) doesn't have secret exits and I was having a lot of fun with it~
I have no problem with the approach you're going for; in fact, you do gather audience and it would also depend on the concept and the preference of the creator in question. I myself am having more fun developing somewhat linear levels nowadays than what I did in the past, and I assume the same applies for most people as well.
To be honest I would value more the gameplay on a hack than the number of secrets it has. Unless it's something where it is worth it, such as JUMP, I'll pretty much focus in completing the levels and sometimes collecting Yoshi Coins only. I consider a linear designer by myself after all, and while a more complex, secret-based is alright, I enjoy a traditional one more.
I'm fine with Linear Hacks. I'm really looking at level design when I play hacks.
For example hacks by "GAMMA V" are all linear but they have that "Super Mario LAND" feel that I adore. Even if they're relatively simple, you'll see they're usually ranked in the 4-5 stars range. It's like playing Super Mario Land in full color.