Dogecoin will never be an ideal cryptocurrency for long term investments. It has a higher inflation than most fiat currencies known to date, which explains the reason why it has struggled to increase in value over time. However, all of this doesn't mean than Dogecoin won't have a future as a usable cryptocurrency. It means that while it may remain used and actively traded in the markets, it will never become a valuable cryptocurrency.
There's no active development or innovation for Dogecoin, but people seems to like it no matter what. If it remains cheap and fast for everyday transactions, then I see no reason for this cryptocurrency to fail in the future. AFAIK, Dogecoin has a huge community behind it, which they'll do whatever it is possible to keep this altcoin alive for the long term. Just my thoughts