Free lunch. The more features, the bigger blockchain. There are tricks to reduce that but the common sense is that if you want to put in a lot of furnitures, your house will necessarily be bigger.
now you heard it, don't complain later that no one told you.
Given the ever-raising blockchain size in the future, light (and mobile) NXT clients should / will be instant on in an Electrum-style manner, meaning that the clients do not download the blockchain but use a remote server to fetch required data. The blockchain will thus be verified by and stored in the decentralized network of tens/hundreds of thousands of NXT nodes.
Anyhow, the blockchain is indeed an issue of BTC, its copies as well as of NXT that results from their decentralized nature. As you may or may not know, the issue is actually described in the original
BTC white paper under
#7 Reclaiming Disk Space. "Once the latest transaction in a coin is buried under enough blocks, the spent transactions before it can be discarded to save disk space. To facilitate this without breaking the block's hash, transactions are hashed in a Merkle Tree, with only the root included in the block's hash. Old blocks can then be compacted by stubbing off branches of the tree. The interior hashes do not need to be stored." -- keeping the entire blockchain on each and every client is not necessary for Bitcoin/NXT to work.