everyone can run a full node .. they just don't get paid for "running" it ..
it's the same with bitcoin .. not all full-nodes get paid ..
if there is a a little reward to run a full-nodes
resume client have a function that reply specifc message automatically, one man or delegate (high pay rate) want to encourage full nodes, he just send a specifc message to backup delegate by random choice , if this delegate is runing a node ,the client reply a message automatically to the sender. if the sender receive the message from backup delegate`s node in a small seconds ,like 5s, it prove this delegate is online,and the network is not bad. he can send some BTS to this delegate as the reward for runing a full node .so this full node can get a little reward , everyone can run a full node when he open computer do other any time.like chat with friends and can join or exit any time.
there some thing must consider ,
1.if a man want to award a full node , the BTS is must his own , maybe he can accept donation ,but how to keep he is honest .
2.award to full node is a action of centralization
3. I don`t konw if can sign a special translation , this translation must comfirm by receiver in a short second , if the receiver don`t comfirm this transltion in a short second ,this transltion would cancel. if have this function , sender just can sign this translation to any backup delegate ( I resume a full node runner must regester as delegate first ,or a special full node account,consider the income of full node is small ,so the regester fee should cheap , maybe two times of account regester fee is better)