Mat,
The are three aspects to using the ".",
one is during typing. Just start your sentence with a period and it becomes a paragraph. then similar to typing bullets "*" you can type a set of paragraphs and they will all behave like paragraphs and be followed by a blank line.
The second is after pasting text content from elsewhere. Being able to look through the text and add a period to transform a line into a paragraph.
The Third is give a larger body of text pasted into a tiddler, using a proposed EditorToolbar button, to select some or all lines and adding the leading period. Looking at the html P tag I discovered it handles nicely the following situations that occur with texts sourced elsewhere; This is after I have placed period at the beginning of each line
.A sentence with more than one line break following it collapses into a single paragraph break
.
.
.
.A short sentence
.a second short sentence without any additional line break above
.
.Lorem Ipsum is simply dummy text of the printing and typesetting industry. Lorem Ipsum has been the industry's standard dummy text ever since the 1500s, when an unknown printer took a galley of type and scrambled it to make a type specimen book. It has survived not only five centuries, but also the leap into electronic typesetting, remaining essentially unchanged. It was popularised in the 1960s with the release of Letraset sheets containing Lorem Ipsum passages, and more recently with desktop publishing software like Aldus PageMaker including versions of Lorem Ipsum
So the P works well in this situation as well.
You can also see that the above is quite helpful now, if you want to improve the text, its easy to see extra line breaks and remove them, but no need to go inserting double enter/carriage returns to make the text look decent. If you do not get around to removing the periods no harm
<p>A sentence with more than one line break following it collapses into a single paragraph break</p>
<p></p>
<p></p>
<p></p>
<p>A short sentence</p>
<p>a second short sentence without any additional line break above</p>
<p></p>
<p>Lorem Ipsum is simply dummy text of the printing and typesetting industry. Lorem Ipsum has been the industry's standard dummy text ever since the 1500s, when an unknown printer took a galley of type and scrambled it to make a type specimen book. It has survived not only five centuries, but also the leap into electronic typesetting, remaining essentially unchanged. It was popularised in the 1960s with the release of Letraset sheets containing Lorem Ipsum passages, and more recently with desktop publishing software like Aldus PageMaker including versions of Lorem Ipsum</p>
Paste the above in a tiddler to see the result if it was "rendered" as proposed.
Regards
Tony