Even though it has been only a month since the 2015 general election concluded, there have been resurging talks about the major boundary changes the Conservatives plan to push through by 2020 (or by the time they are forced to call an early election, which is a strong possibility given their small majority of 10 and the inevitability of by-elections during the next few years). However, given the current rules of these planned changes (set in 2013), the necessity to create large numbers of cross-boundary seats as a result, and the practical issues, I believe these are three significant reasons why those major boundary changes may never take place or might only take place in a substantially modified form:
1. These boundary changes would raise substantial objections from many Conservative backbenchers, and of course all opposition parties in the House of Commons. The Conservatives hold 11 seats in Wales (more than their small majority!)which, being considerably under the allowable electorate under the 2013 Electoral Administration Act (which required this major boundary review), will be redrawn or carved up and end up moving a lot of areas with substantial Labour support into these seats (many of which are not that safe at all). These changes could also leave the Conservatives without a viable winnable seat anywhere in Scotland due to how well the SNP performed across all of Scotland, even in the three constituencies they did not win. Labour, the Liberal Democrats, the SNP, Plaid Cymru, and the Green Party will be even more aggrieved by the boundary changes, because the South East and South West will lose fewer seats than the regions of the North and the Midlands.
2. The reduction in seats will necessitate large numbers of cross-county seats, which will undoubtedly raise substantial local objections especially in rural areas. The most worrying possibility is a cross-Tamar seat between Devon and Cornwall, which will substantially harm the cause of Cornish self-determination. Other major problems will arise if cities end up with vulgar fractional quotas necessitating messy half-urban, half-rural seats (one possibility I have imagined is Bristol East and Kingswood)
3. The final changes may be unworkable in practice for other reasons. Some large urban wards (e.g. in Birmingham) may need to be split in order for these quotas to be met, which will cause problems for reorganising polling stations for proposed constituencies. The fact even more constituencies will cross between authorities will also create additional expense for local authorities and election staff.
The best way to ensure fairness in representation is not to redraw boundaries, but to abolish first past the post altogether and introduce proportional representation. Proportional representation will also be more efficient, be easier for electoral officials, and will result in fewer and/or less frequent boundary changes as well.