S&W would have to do some serious revision to the L frame to make it a 5 shot 45. I have 3 5 shot L frame 44s (69, 696 and 396) and good calipers and mics. I bought the 69 first with the thought of making it into a 45. But, reaming it to 45 would leave the outside of cylinder paper thin. Between chambers would be fine. Taurus can do it because the have a smaller ratchet OD and chambers are closer to center of cylinder. For S&W to fo this they would need to make a smaller ratchet and because of this move the hand and its frame slot closer to center. To do this would take thinner action parts or offset hand. PLUS, moving the chambers in would mean they would need to lower the barrel in the frame to match. Which would mean a thinner area where yoke fits under barrel or a revised yoke.
The other alternative is to widen the frame window from top to bottom so a larger OD cylinder, Which would mean considerable reworking of the frame stamping and the pivot points of bolt, trigger, hammer etc.
NOT going to happen. IMHO