As one might expect from the Ministry of Justice, the main preoccupation seems to be saving money whilst retaining physical wills for the least possible time necessary to satisfy legal requirements (eg challenges to a will). As MollyC indicates, once these functional (legal) requirements have fallen away, these documents should be handed to TNA who are already expert in preserving old documents.
The MoJ shows how out of touch it is with the genealogical community by this statement:
... paper wills have been kept continuously since 1858, which is over 160 years, despite the fact that the capacity to challenge a will, for which want of witnesses and other evidence, would likely have expired after a tiny fraction of that time [...] However, whilst that may be the case, the Government also considers that the emotional value of such original documents to relatives and to society is likely to diminish over time and, importantly, the question of retaining a digital version of wills in perpetuity need not be considered in isolation.
paras 29 and 30 of the consultation
Realistically, of course, genealogists rarely get to see and touch the original (post 1858) wills. If we order one from the outsourced HMCTS service, we just get a scanned or digital photograph of the document. To that extent this proposal would make very little difference. But the proposed wholesale destruction of these worthy documents just to save £4.5M pounds is nothing short of heritage vandalism.
