HTML can be made to look nice, which means that it will go over well with suits. However it suffers from bit-rot, displays differently on different platforms, is more complex for standard text tools to process, etc. Therefore technical types tend to see HTML email in the same category as Word and Powerpoint attachments - a sign that the sender is not technical and does not have a clue about how the technical community works. It may not look as pretty to you, but it will go over a lot better with us. Actually the Open Source community has a lot of people who are very distrustful of the standard Fortune 1000.
Any guidelines are opinions based on current goals, ideology, and position.
Actually the continuing proliferation of licenses is generally agreed to be undesirable. People seem to want to create licenses that protect themselves in some way. But if you take code licensed under two different licenses designed that way, you usually are unable to borrow. That reduces the ability to use opened code, or to easily add interesting functionality to it. My strong advice would be to carefully consider what it is you wish to accomplish and use an existing license.