I've run a setup something like this (not using the storage solution described in the article, but the principle of the thing is the same) and I've had fairly good results. The main things to consider in my estimation are:

1) Your Myth setup. I use a slave setup for each TV, with a single Master media server that does all of the capture of content. This way I can us as small a box as possible for the part that is out in public and just put the rest in the 'server closet' as it is called. If you follow this model, and the storage is close (in a network sense) to the primary media server you might be ok.

2) Network impact. Having a lot of data from the NAS to your Myth box for the purposes of using the TV could have a impact on your network. You just might need to take some steps to isolate the network that the NAS is running on from the one that you'll be using to browse the internet if you are anything like me.

3) What do you really want to backup. I purposefully don't try and backup everything, just the things I don't already have some backup for. Thus, the DVDs I've pulled to the disk don't get backed up because the DVD is the backup. Just my personal data and this lightens the load a bit. (I'm primarily doing that because I'm in the States, and we have really bad upstream rates on most broadband so I have to be more selective.)