Here goes:

1) If a line starts and ends with a pipe, it's a table row. Cells are separated by pipes

 |a1|b1|c1|
 |a2|b2|c2|

displays

2) empty lines separate tables

 |a1|b1|c1|

 |a2|b2|c2|

displays

3) If a cell ends with more than one pipe, it's a column span:

 |a1||c1|
 |a2|b2|c2|
 |a3|b3||
 |a4| |c4|

displays

4) If a line starts with more than one pipe, it's continuing rowspans from above:

 |a1|b1|c1|
 |||c2|
 ||b3|c3|
 |||c4|

displays

5) treat

 |a1
 ||b1
 |||c1|d1|e1|

same as

|a1|b1|c1|d1|e1|

This means that

 |mammalia
 ||carnivora
 |||canis
 ||||dog|house|woofs|
 ||||wolf|woods|yelps|
 |||felis
 ||||cat|house|meows|
 ||||lynx|woods|hisses|
 ||rodenta
 |||ratus
 ||||brown rat|sewer|squeaks|
 ||||black rat|middle ages|plagues|

produces

5) Headings are allowed, and are treated as header cells:

 |==Nowheria==||
 |===Capital===|Backendsville|
 |===Surface area===|small|
 |===People===|many|

displays

• Only one paragraph per cell.
• Row spans can be specified only for leftmost cells in the table

I don't think either is very important - most tables don't need multiple paragraphs per cell and row spans are much more useful on the left side than anywhere else. If any of it is needed, there's < table > to fall back on.

• Use spacing to specify alignment.

 |left | center | right|

• Caption row, including alignment for the table.

maybe make it should look like section titles?

  |=caption=|
  |a1|b1|c1|
  |a2|b2|c2|