I have 38 DVD/Blu-ray hybrids.
Some I have removed the DVD and replaced with a Blu-ray, others have both Blu-ray and DVD. It depends if there is enough room for both in the SteelBook.
e.g. Jurassic Park UK SteelBook has room for 4-Discs, the 3 movies and a bonus disc, so I just replaced the Movie discs and left the bonus disc in there to fill the space lol. Also the Swedish DVD SteelBook of The Spirit has only one disc, so I have now got just the Blu-ray release in there.
A lot of the DVD SteelBooks are 2-Disc releases, so I file away the Special Features Disc and replace with a Blu-ray.
Most of my DVD SteelBooks are from various regions R1 and R2 mostly and its a little annoying to have a DVD with "Disc 1" printed on it, so I sometimes replace these with a R4 DVD which is my region.