I am considering a transition into the land of 29er's but I am trying to amortize the costs.

I currently have a kelly deluxe that I really enjoy riding. I was thinking about how to make it even more enjoyable and this thought came to my mind

ditch the sid, get a rigid 26" disc spec. fork, and stick a 29er wheel in there. There is plenty of clearance to the crown for the 29" wheel, and the increased radius will offset the rigidity.

Also, when it comes time to move up to full on 29ers, Ill be one step closer.

Do you see any problems with this?

Welcome to the forums!

It's been done before. It works well, at least it did for me. Buy the (often used for this) cheap Dimension MTB Disc fork. It's 410mm, and won't mess up the geometry replacing a SID when sticking in a 29" front wheel. Long shot option is a Surly 1x1 fork. Near the same geo, higher price. Not disc-only though.
Plenty stock 29" wheels sold in the classifieds here. You may manage to keep it under $150 if you already have the disc brake.

My first ownership in the 29" world was this, late 2001 I think.
http://forums.mtbr.com/attachment.php?attachmentid=2182&d=1075399171