Endless pool OK, but if you really want to make it a great technique tool you\'ll need one glass sidewall and a glass front end wall, so you can video the stroke properly. Add in some readily available swim coach software to analyse and overlay strokes, and you\'ve got a really useful, and rare tool.
They\'re also really good if you plan on selling wetsuits!
Another suggestion would be to have the faciltiy arranged so that you can do an indoor triathlon, without having to go up and down stairs or open and close doors. You could then race as many athletes as you have spin bikes, or more usefully, run brick sessions, staggered if you have more participants than spin bikes, as it\'s very difficult to get satisfactory T1 practice elsewhere.
Some gyms now have indoor running tracks (Total Fitness in Preston has one, and I\'m sure some posh gyms down south will too). One of these would be better than endless treadmill sessions, and would allow better group training, but you\'d need plenty of space.