That's a brilliant question lljdma06. i've been asked this but not in the way you have
here's goes...
Q. have you ever thought about scape development in terms of years rather than months?
A. yes many times, but in my high tech systems which include double dosing EI, co2 and high light plants grow extremely quick. for example in this tank i had to cut A. reineckii in the first week and a half.
I get a buzz or a satisfaction almost from the quick growth of plants and the "instant" effect is brings within the scape.
Q. so I'm not quite understanding you when you say "as long as the stems allow". Is this pertaining to growth or longevity?
A. I'm not sure if your aware, but i did a scape for my local LFS. (i'll add pic) now this scape contained rotala rotundifolia. i maintained this tank for 6 months. the stems required several trimming sessions to get the desired effect, but then came the time when lower portion of stems became ugly. I had the foresight to hide the lower parts with blyxa, but soon the undesirable part became visible ultimately producing an unsightly line. they never grew unruly,the trimming saw that they were uniform and tidy at the crowns.
with this quick turnover, customers did make me aware that they loved to watch the scape "grow" over a short period of time.
of course, with a tank design that has layers (stems) lets say the Dutch style, it would be possible to keep stems for much longer, and I know it's possible. but as amano says, don't use stems in a long term scape.
this is a long term scape i've done for the same shop....no stems.
Another point for my fast turnover is the fact that it gives me the chance to learn many plants and there effects very quickly. so I can take this knowledge into future scapes.
One last point is, if I tried a long term scape at home, it would slow my learning down considerably unless I had several tanks....which i don't...i wish!n (hence the LFS tanks to help me learn)
I'm sure i've missed things off here lljdma06, but I think you'll get where I'm coming from. there's some great questions you've asked and if i think of other things I'll add them.