I'm doubting that he'll be accepting directly payments with Dogecoin but it's likely that he'll allow some third party services that will be integrated with Twitter to accept payments in doge or any other crypto.
It can be that maybe Elon Musk wants to keep a different profile with Tesla and other companies he runs from Twitter, that is likely why he will accept Dogecoin as means of payment on his Twitter platform but not on all others. He was twitting about Dogecoin long before he bought Twitter and I do not see why he will want to stop now. On the announcement that he had bought it, price of Dogecoin went up and gave holders a new faith in the coin. It is a good investment to buy that coin now as I do not see it dumping. Buy, wait and sell when you think price has increased enough.