I apologise if this has been discussed address already but @davef have you considered a 3-way sierra bookshelf for people who want to upgrade but cannot manage to get Sierra Towers.
Or asked differently have considered building something that would be next step up from sierra-2(which is fantastic speaker btw) for people who couldn't quite manage the real estate for sierra towers.
PS: I am not sure the next step from sierra 2 needs to be a 3-way speaker but ST is one so i assumed the next step up would be a 3-way ...