As an advocate for the addition of Professor E. Gadd to the franchise to use the patented Poltergust vacuum and his various other gadgets that he let Luigi use to aid him on his quest you would think Luigi getting such a remodeling using this style is whole lot more realistic than the actual inclusion of the Professor. Now while that is very true, the developers of the Smash series are keen on keeping some of Luigi's attacks similar to that of his brother Mario's.
I'd say the most likely scenario for this situation would be for the Poltergust to be used as a down or side B attack similar to how they implemented Mario's F. L. U. D. D attack from Super Mario Sunshine in Brawl. Maybe, when the Poltergust is out and ready to go your attacks differ for A or B than opposed to when it's not unleashed entirely. You may be able to use other tools such as the Spectroflash and Dark Light once you're in full ghost catching mode.