I must admit the thought shortly came to light but then I remembered that I have several vintage spring reverbs in my studio. ;P
Well, I specifically want one IN the A4 to draft things out and get proper fx send handling for spring reverberated carpenteresque soundgoodness. If you know what I mean.
The A4 can shine in different lights if you pull the internal effects and use e.g. a roland space echo, or some true electro mechanical spring reverb. Also gets some different character with other digital reverbs like eventide space etc... etc... to have at least some different characteristics in the box would be a great improvement..