Is USGS planning to produce a web map service version of US Topo map layers for GIS applications?
Not for US Topo maps. These maps are derived from GIS data and packaged in traditional map form for the benefit of non-specialist users. Most of the data used to make US Topo maps are available from USGS through map services and staged datasets. USGS map services include a topographic base map service, USGSTopo, that is a close approximation of traditional topographic map presentation at medium scales. This service is built from many of the same sources as US Topo maps, but is designed for GIS use.
We may create map services for the Historical Topographic Map Collection, or perhaps a subset of that collection. However, this is a low program priority, and will not happen until at least 2016.