I'm researching things and came across your question although it's from a few weeks ago.  Yes, it's possible to have no transaction fees.  A lot of projects don't do it for a couple of reasons: 1) They want to reward the consensus miners through the transaction fees, or 2) They are concerned about the possibility of spam on the network.

I'm invested in Skycoin and they have come up with good solutions to both issues: 1) They have implemented a new consensus model (Obelisk) that eliminates the need for traditional miners which as we've seen with other projects leads to centralization.  2) People who hold Skycoins in their wallet earn 1 CoinHour per hour for each coin that is held in the wallet (similar to Gas).  CoinHours are burnt when transactions are sent, so the CoinHours serve as the congestion-reduction mechanism instead of spending actual Skycoin.  CoinHours will also be used to purchase bandwidth on the Skywire internet, and will also have other uses that haven't been rolled out yet (spendable in blockchain games, ability to trade them for Skycoin or other coins, etc).