I just killed syllabics :Þ

So I take some of that back.  I've just killed off syllabics altogether, so you can ignore the bit about them being their own letter à la icelandic and all that.

C[+sonorant,+syllabic] → C[-syllabic]a

Syllabic sonorant consonants become non-syllabic and are followed by -a.

swistr → swistra (sister)
rign → rigna (rain)

It also has some interesting implications for verbs:

dūn, stēn, gīn - no syllabics here.  But:

wisan > wisn > wisna
waírþan > werðn > werðna

Here's also a nifty twist for Class 1 weak verbs:

wiljan > wilin