I have way too many feelings about this.
I know it's irrational so I'm not going to keep this minimal. I keep visiting astro.com and looking at my chart to make sure they haven't updated it.
It seems to me the definitions of the signs have evolved over the years - and abrupt change seems to negate that. Maybe the sun-signs have "progressed" like a person's chart will? But astrology does respond to scientific discovery. Classical "planets" included the sun, moon, mercury, venus, mars, jupiter and saturn. Only since the invention of the telescope has Western astrology incorporated Uranus, Neptune and Pluto. Pisces (my sign (dammit)), was traditionally ruled by Jupiter, but modern astrologers consider Pisces to be ruled by Neptune - which was only discovered in 1846.
So I'm guessing this issue - which appears to have sprung from the off-hand statements of an astronomy professor who wasn't speaking about astrology - will be incorporated into modern astrology as time passes. I'm looking forward to seeing what it will be like in 10 years. It seems like a major consciousness shift to me, but then I'm more attached to astrology than most people.