We use text-align:left because neither the dir="auto" nor the unicode-bidi:plaintext specification states whether text-align:start and text-align:end should obey the paragraph direction or the direction property in a unicode-bidi:plaintext element. The ...! paragraph, being neutral, is supposed to be displayed LTR (i.e. as ...!, not as !...) despite both the paragraph before it and the paragraph after it being all-RTL, which makes the element as a whole RTL.
@123! א ...! א
@123! א ...! א