If the Summoner was to be introduced, it would need some changes.
First, let's look at it. ERPPC, LBX10, LRM15. Not a lot of weaponry, below-average armor, but great speed and jump capacity. The Summoner originally had an additional SRM6 (notice the 3-missile pods on each leg?) but that got removed when it was introduced proper in CBT.
So I'd say reintroduce the SRM6 (to make up for the retarded minimum range on Clan LRMs since summoner is INTENDED to use it's LRM at point blank aswell in CBT, as do many other designs) and upgrade the LBX to a 20-series. It's the only way I can see this design to become useful in MWLL.