How do axon terminals report to the soma?
We can consider the classical example of Long Term Potentiation. 

CREB is a transcription factor which is activated during LTP by phosphorylation. 

Your reasoning about the delay between signal and transcriptional response is correct and thats why neurons have local translation factories near the dendritic spines and gene regulation (fast responses) is mostly post-transcriptional. (there is no article which says exactly so but you can refer so some articles  which report that miRNA-repressed genes are reactivated upon certain signals. They hint that post translational regulation is very important in neurons) 

http://www.cell.com/neuron/abstract/S0896-6273%2809%2900939-8

http://nar.oxfordjournals.org/content/40/11/5088