Yes, I use LibreOffice for plain text, or encoded text, on many different types of projects. For all the others, I use "Kate" on my "default" Ubuntu system.
Beyond the "plain text file" question, there is another question here, if I read the posts correctly.
You asked how to use your template "system wide". What do you mean by "system wide". All users on a single PC, or all PCs [Windows, Mac, or Linux] on a network?
If on many networked PCs, were you intention to manually set up the network PCs, or to have the template on a network server and each LO package go out to the "networked drive" for that default template.
I know that there are a lot of business networks that want each user's computer to have the same packages on it and maybe even use the same templates for their documents. This is an important question for LO to be part of a business network. Can you change the "Tools>Options>LibreOffice>Paths>Templates" to a networked drive or a file server? If so, how is that done, with examples? I do not remember if there are any references for this type of thing in the "guides" or on the wiki pages. Since this is one of the business "options" that may be required to deploy LO to their network, we need to have some good documentation for this, and other network deployment, question[s].
Since I do not use a networked drive or file server, I cannot test out any examples that I might be able to give.