Over the years, many people have thrown themselves at the issue of spelling reform. Concerned about the irregularity and non-phonetic nature of English spelling, clever people have devoted imense amounts of effort to the cause. But over the last two hundred years, the results have been negligible. The last successful attempt to impose new spellings by fiat was American Noah Webster's speller of 1785: he managed, in a febrile political climate which was very receptive to the idea of change in general and change to things inherited from England in particular, to impose some minor changes to words like colour/color and theatre/theater. Since then, all efforts have come to naught. And they will continue to come to naught.
Leave aside the inability of reformers to agree amongst themselves about the reform they want. Leave aside doubt about the claim that phonetic spelling is actually necessary. Instead, let us assume that the basic premise of the reformers, that there should be a consistent relationship between sound and spelling, is true, and that they have such a reformed orthography complete ready for adoption. It will fail. Whatever the proposal, it will fail.
Regional Division
Firstly, the proposal will inevitably involve the concept of some form of standard accent that the reformed spelling relates to. In any significantly sized country which speaks English, there is a variety of regional accents. Not only will these have different pronunciations for the same words, but words which are homophones in one accent may not be in another. Londoners might pronounce poor and pour alike; Scotsmen will not; some or all of duel, dual and jewel may be homophones depending upon who is talking. Any spelling reform will tend to privilege one particular accent, usually something close to "RP", and will become almost as arbitrary as existing orthography the further from that accent one moves. This will make the reform unacceptable to many, including parts of the English speaking world which have distinctive accents and already have separatist tendencies (Scotland, Quebec). Separatist politicians will denounce the new spellings as an attempt to impose a national accent; the argument will be very hard to refute while still providing a coherent argument for the reform. If the spelling is to be national and to be phonetic, there must be a national accent. If regional accents are to be preserved, the spelling cannot be phonetic.
Age and Class Division
Secondly, even if the reform could be "sold" throughout a country, the only plausible way to introduce it would be via schools. Many schools would simply refuse to accept such a change, and these schools would tend be those which are already privileged. They would tell parents that the reform constituted "dumbing down" and that, even if it succeeds, the new spelling will be seen as low status. In addition, literate parents would not welcome such a reform, as it would exclude them from helping their children, and they would work actively to undermine it. It is hard to see how the result would not be a two-tier English, with children of affluent, educated parents retaining old spellings while the new spellings become the hallmark of deprivation. Newspapers and other publishers would not change, as the market for new spelling would be tiny in comparison with that for the existing orthography, and the new spelling would not achieve critical mass.
International Division
Thirdly, unlike in 1785 when international communication was by sailing ships, and books were published locally on local presses with local spelling, English is now an international language. There is no central body which manages English, and there is no plausible way that such a body could be set up. Therefore, any country which altered its "official" spelling (even accepting that it could impose such a thing on its own population) would be cutting itself off from the rest of the English speaking world. Much of English's value lies in its role as a lingua franca, and complicating that by adding a new set of spelling rules (which would, of course, not be phonetic in the heavily accented English spoken in countries where it is the second or third language) would damage this.
Objections to these Arguments
Reformers point to successful, or at least partially successful reforms, in other languages. The German reforms of 1996 would be the most relevant, but do not answer my objections. Firstly, the reforms aimed at increasing phonetic correspondence were minor, so the issue of accent does not arise (or, at least, arises no more than in any other spelling system for German). The changes do not seek to impose a standard accent, and the spellings which were altered were brought into closer correspondence with almost all native speakers' accents. Secondly, the changes were small, of a scale akin to Webster's of 1785 rather than the extensive changes proposed by reformers of English, and do not create a very obvious before and after language. Thirdly, German is dominated by one country, Germany, which has a particularly centralised education system with a very strong degree of control, so the issues both of refusal by some schools and of international division do not arise.
Conclusion
Spelling reform of English will not happen, no matter how excellent the arguments or how polished the proposal. It would not be acceptable to people who do not speak RP, it would not be possible to mandate its use on any large scale, and it would not gain any traction outside the first country to adopt it. It is a waste of intellectual effort to work on reforms without answering these objections.