It would be great if web pages saved via Safari's offline reader functionality could be loaded in Pleco's web browser. I'm guessing Apple does not provide the necessary APIs that allow this, but I thought I'd ask nonetheless.
Sadly not something they provide APIs for at the moment, no. We could possibly integrate with a third-party API like Instapaper or Read It Later but we haven't really had enough requests for this yet to consider doing that. (we could also theoretically add a "Share with Pleco" app extension for links - that would be a relatively easy one to write)