Shape5

My personal suggestion is to release template source in more formats than PSD only.

I can understand why you're using PSD, and it's perfect for you and for customers too if they have certain software suites on their computer

But until you have them, will be hard to customize and/or edit the template design

Consider that these programs are all but cheap (most of the buyers can't afford these expenses, in my opinion) and  using a trial version gives you the chance to customize things until trial expire (and this is unacceptable)

Realeasing the template source under a file format that can be handled with free software will be really a plus (and leaves in customer pocket's the money for renewing their subscription for the next years)

GIMP's (http://www.gimp.org/) native format will be a great choice (cross-platform, open source, etc)
GIMP can already open and modify PSD also, but text will be rendered as bitmap and won't be customizable
Maybe in the future the developers will add support for text interpretation as object

Another great free tool is Inkscape (http://www.inkscape.org/) that works in SVG and last but not least, OpenOffice's Draw (http://www.openoffice.org)with it's OpenDocument format.

I really have no idea of how much work this "cross-release" will take and how could be obtained...

Paint Shop Pro (PSP) version 7 can't open the psd files, claims they are corrupt. Version 9 of PSP can display the layers (and there is a lot of them), yet claims some features are not supported. I have not had a need to upgrade to PSP X or later, so I don't know if they will open and display the psd files correctly.

One format that you may want to consider is TIFF. It is popular in the publishing and printing industries (I don't mean desktop publishing, though I am sure a few do use it).  The printing and publishing industry likes it because you can have a number of pages, and each page can have a number of images/layers with it. Most of the time the first image in a page will be a composite, showing how it should look when printed, with each image/layer showing a different color, such as magenta, cyan, yellow and black. In a special project where I helped an engineering firm with data entry they would have an overall blueprint as the first page, the framing as page 2, gas lines as page 3, etc. As they got revisions they would insert it as the first image for the page, pushing the older revisions down in the order. This could be adapted to work with the current psd files, and bring a bit more order to them.

Just throwing out a wild-hair idea.