I think they will build new services on top of their 3rd generation blockchain. This TechCrunch article is a pretty good source to read if you want to know more about their plans. An interesting point though is that they are keeping 52% of all GRAM supply. The following is a quote from the article.

The white paper also makes clear that four percent of the supply of Grams (200 million Grams) will be reserved for Telegram’s development team with a four-year vesting period. Telegram also plans to retain “at least 52 percent” of the entire supply of the Grams cryptocurrency to protect it from speculative trading and maintain flexibility. The remaining 44 percent will be sold in both the public and private sale.

Thoughts?